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>

scripts/docker-build.sh

@@ -0,0 +1,93 @@
+#!/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."