feat: containerize build environment with Docker

- docker/Dockerfile: multi-stage image (linux-builder + windows-builder)
  - linux-builder: Ubuntu 22.04 + OpenCV/LibRaw/Qt6 + GTest
  - windows-builder: MXE cross-compilation (x86_64-w64-mingw32.static)
    with OpenCV4, LibRaw, Qt6 for Windows .exe output
- docker-compose.yml: services for linux, windows-build, shell
- scripts/docker-build.sh: convenience wrapper
  - linux|windows|all targets
  - --no-cache, --run flags

Usage:
  ./scripts/docker-build.sh linux --run
  ./scripts/docker-build.sh windows

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

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+name: photo-converter
+
+services:
+
+  # ── Linux-Build (CLI) ────────────────────────────────────────────────────
+  linux:
+    build:
+      context: .
+      dockerfile: docker/Dockerfile
+      target: linux-builder
+    image: photo-converter:linux
+    volumes:
+      # Input-Bilder aus lokalem import/ Ordner einbinden
+      - ./import:/project/import:ro
+      # Konvertierte Bilder in lokalen output/ Ordner schreiben
+      - ./output:/project/output
+      # Konfiguration überschreibbar
+      - ./config.ini:/project/config.ini:ro
+    command: ["--batch", "--config", "config.ini"]
+
+  # ── Windows Cross-Compilation ────────────────────────────────────────────
+  windows-build:
+    build:
+      context: .
+      dockerfile: docker/Dockerfile
+      target: windows-builder
+    image: photo-converter:windows-builder
+    volumes:
+      # Windows-Build-Ergebnis in lokales dist-windows/ schreiben
+      - ./dist-windows:/project/dist-windows
+    # Nur bauen, kein Entrypoint
+    entrypoint: ["/bin/bash", "-c"]
+    command:
+      - |
+        echo "Windows-Build abgeschlossen."
+        echo "Ergebnis in: /project/dist-windows"
+        ls -lh /project/dist-windows/bin/ 2>/dev/null || echo "(kein bin/ Verzeichnis)"
+
+  # ── Interaktive Shell (Debugging) ────────────────────────────────────────
+  shell:
+    build:
+      context: .
+      dockerfile: docker/Dockerfile
+      target: linux-builder
+    image: photo-converter:linux
+    volumes:
+      - ./import:/project/import:ro
+      - ./output:/project/output
+      - ./config.ini:/project/config.ini:ro
+    entrypoint: ["/bin/bash"]
+    stdin_open: true
+    tty: true

docker/Dockerfile

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+# ─────────────────────────────────────────────────────────────────────────────
+# photo-converter — Multi-Stage Build Image
+#
+# Stages:
+#   base            — Gemeinsame Tools (cmake, ninja, gcc)
+#   linux-builder   — Linux-Build mit OpenCV, LibRaw, Qt6
+#   windows-builder — Windows Cross-Compilation via MXE + MinGW-w64
+#
+# Verwendung:
+#   docker build --target linux-builder  -t photo-converter:linux   .
+#   docker build --target windows-builder -t photo-converter:windows .
+# ─────────────────────────────────────────────────────────────────────────────
+
+# Ubuntu 22.04 LTS: MXE-Pakete sind für focal/jammy verfügbar
+ARG UBUNTU_VERSION=22.04
+FROM ubuntu:${UBUNTU_VERSION} AS base
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    TZ=UTC
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    # Build-Tools
+    cmake \
+    ninja-build \
+    build-essential \
+    pkg-config \
+    git \
+    # Hilfswerkzeuge
+    wget \
+    curl \
+    unzip \
+    zip \
+    ca-certificates \
+    gnupg \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /project
+
+# ─────────────────────────────────────────────────────────────────────────────
+# Stage: linux-builder
+# Linux-Build mit OpenCV, LibRaw, Qt6
+# ─────────────────────────────────────────────────────────────────────────────
+FROM base AS linux-builder
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    # OpenCV
+    libopencv-dev \
+    # LibRaw
+    libraw-dev \
+    # Qt6
+    qt6-base-dev \
+    libqt6widgets6 \
+    libxkbcommon-dev \
+    # GTest für Tests
+    libgtest-dev \
+    # OpenGL (Qt-Abhängigkeit)
+    libgl1-mesa-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY . /project
+
+# Standard: Release ohne GUI (GUI benötigt X11/Display)
+RUN cmake -B build -G Ninja \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DBUILD_GUI=OFF \
+        -DBUILD_TESTS=ON \
+    && cmake --build build --parallel "$(nproc)" \
+    && ctest --test-dir build --output-on-failure
+
+ENTRYPOINT ["./build/photo-converter"]
+CMD ["--batch", "--config", "config.ini"]
+
+# ─────────────────────────────────────────────────────────────────────────────
+# Stage: windows-builder
+# Windows Cross-Compilation via MXE (MinGW-w64 + statisch gelinkte Deps)
+# ─────────────────────────────────────────────────────────────────────────────
+FROM base AS windows-builder
+
+# MXE Repository einrichten
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    apt-transport-https \
+    lsb-release \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN curl -fsSL "https://pkg.mxe.cc/repos/apt/client-conf/mxeapt.gpg" \
+        -o /etc/apt/trusted.gpg.d/mxeapt.gpg \
+    && echo "deb [arch=amd64] https://pkg.mxe.cc/repos/apt focal main" \
+        > /etc/apt/sources.list.d/mxeapt.list
+
+# MXE-Pakete: OpenCV + LibRaw + Qt6 (statisch, x86_64)
+# Hinweis: Initial-Download ~3 GB, dauert je nach Bandbreite 10-30 Min.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    mxe-x86-64-w64-mingw32.static-cmake \
+    mxe-x86-64-w64-mingw32.static-opencv4 \
+    mxe-x86-64-w64-mingw32.static-libraw \
+    mxe-x86-64-w64-mingw32.static-qtbase \
+    mxe-x86-64-w64-mingw32.static-cc \
+    && rm -rf /var/lib/apt/lists/*
+
+ENV MXE_PREFIX=/usr/lib/mxe/usr/x86_64-w64-mingw32.static \
+    PATH="/usr/lib/mxe/usr/bin:${PATH}"
+
+COPY . /project
+
+RUN cmake -B build-windows -G Ninja \
+        -DCMAKE_TOOLCHAIN_FILE=cmake/toolchain-mingw64.cmake \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_PREFIX_PATH="${MXE_PREFIX}" \
+        -DCMAKE_INSTALL_PREFIX=/project/dist-windows \
+        -DBUILD_GUI=ON \
+        -DBUILD_TESTS=OFF \
+    && cmake --build build-windows --parallel "$(nproc)" \
+    && cmake --install build-windows
+
+# Ergebnis: /project/dist-windows/bin/photo-converter.exe
+ENTRYPOINT ["/bin/bash"]

scripts/docker-build.sh

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+#!/usr/bin/env bash
+# docker-build.sh — Baut photo-converter in Docker
+#
+# Verwendung:
+#   ./scripts/docker-build.sh [linux|windows|all] [--no-cache] [--run]
+#
+# Optionen:
+#   linux      Linux CLI-Build (Standard)
+#   windows    Windows Cross-Compilation via MXE
+#   all        Beide Targets bauen
+#   --no-cache Docker-Cache ignorieren
+#   --run      Nach dem Build direkt ausführen (nur linux)
+
+set -euo pipefail
+
+RED='\033[0;31m'; GREEN='\033[0;32m'; BLUE='\033[0;34m'; NC='\033[0m'
+log_info() { echo -e "${BLUE}[docker]${NC} $*"; }
+log_ok()   { echo -e "${GREEN}[ok]${NC}    $*"; }
+log_error(){ echo -e "${RED}[error]${NC} $*"; exit 1; }
+
+TARGET="linux"
+NO_CACHE=""
+RUN_AFTER=0
+
+for arg in "$@"; do
+    case "$arg" in
+        linux)     TARGET="linux" ;;
+        windows)   TARGET="windows" ;;
+        all)       TARGET="all" ;;
+        --no-cache) NO_CACHE="--no-cache" ;;
+        --run)     RUN_AFTER=1 ;;
+        --help|-h) sed -n '2,9p' "$0" | sed 's/^# \?//'; exit 0 ;;
+        *) log_error "Unbekannte Option: $arg" ;;
+    esac
+done
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+cd "$PROJECT_ROOT"
+
+command -v docker &>/dev/null || log_error "Docker nicht gefunden. Installieren: https://docs.docker.com/get-docker/"
+
+mkdir -p output dist-windows
+
+build_linux() {
+    log_info "Baue Linux-Image (photo-converter:linux) ..."
+    docker build $NO_CACHE \
+        --target linux-builder \
+        -t photo-converter:linux \
+        -f docker/Dockerfile \
+        .
+    log_ok "Linux-Image gebaut"
+
+    if [[ $RUN_AFTER -eq 1 ]]; then
+        log_info "Starte Konvertierung ..."
+        docker run --rm \
+            -v "$PROJECT_ROOT/import:/project/import:ro" \
+            -v "$PROJECT_ROOT/output:/project/output" \
+            -v "$PROJECT_ROOT/config.ini:/project/config.ini:ro" \
+            photo-converter:linux \
+            --batch --config config.ini
+        log_ok "Konvertierung abgeschlossen. Ergebnisse in: output/"
+    fi
+}
+
+build_windows() {
+    log_info "Baue Windows-Cross-Compilation-Image (photo-converter:windows-builder) ..."
+    log_info "Hinweis: Erster Build lädt ~3 GB MXE-Pakete herunter (~20-30 Min)"
+    docker build $NO_CACHE \
+        --target windows-builder \
+        -t photo-converter:windows-builder \
+        -f docker/Dockerfile \
+        .
+    log_ok "Windows-Builder-Image gebaut"
+
+    log_info "Extrahiere photo-converter.exe ..."
+    mkdir -p dist-windows
+    docker run --rm \
+        -v "$PROJECT_ROOT/dist-windows:/project/dist-windows" \
+        photo-converter:windows-builder \
+        -c "cp -r /project/dist-windows/. /project/dist-windows/ && echo 'Fertig'"
+
+    log_ok "Windows-Build abgeschlossen: dist-windows/"
+    ls -lh dist-windows/bin/ 2>/dev/null || true
+}
+
+case "$TARGET" in
+    linux)   build_linux ;;
+    windows) build_windows ;;
+    all)     build_linux; build_windows ;;
+esac
+
+log_ok "Fertig."