feat: fix Docker Windows cross-compile and add color grading

- Fix MXE GPG key import (gpg --dearmor + signed-by)
- Fix MXE package names (opencv4→opencv)
- Use Ubuntu 20.04 base for windows-builder (MXE focal compatibility)
- Install CMake 3.20+ from Kitware PPA for windows-builder
- Add ColorGradingParams.h for color grading pipeline
- Update ColorCorrector, AppConfig, MainWindow, ImageData, CliRunner

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

docker/Dockerfile

@@ -11,9 +11,8 @@
 #   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
+# Ubuntu 22.04 LTS für Linux-Build
+FROM ubuntu:22.04 AS base
 
 ENV DEBIAN_FRONTEND=noninteractive \
     TZ=UTC
@@ -73,27 +72,46 @@ CMD ["--batch", "--config", "config.ini"]
 # ─────────────────────────────────────────────────────────────────────────────
 # Stage: windows-builder
 # Windows Cross-Compilation via MXE (MinGW-w64 + statisch gelinkte Deps)
+# MXE-Pakete sind für Ubuntu 20.04 (focal) gebaut → eigene Base nötig
 # ─────────────────────────────────────────────────────────────────────────────
-FROM base AS windows-builder
+FROM ubuntu:20.04 AS windows-builder
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    TZ=UTC
 
-# MXE Repository einrichten
 RUN apt-get update && apt-get install -y --no-install-recommends \
+    ninja-build \
+    build-essential \
+    pkg-config \
+    curl \
+    ca-certificates \
+    gnupg \
     apt-transport-https \
-    lsb-release \
     && rm -rf /var/lib/apt/lists/*
 
+# CMake 3.20+ von Kitware (Ubuntu 20.04 liefert nur 3.16)
+RUN curl -fsSL https://apt.kitware.com/keys/kitware-archive-latest.asc \
+        | gpg --dearmor -o /usr/share/keyrings/kitware-archive-keyring.gpg \
+    && echo "deb [signed-by=/usr/share/keyrings/kitware-archive-keyring.gpg] https://apt.kitware.com/ubuntu/ focal main" \
+        > /etc/apt/sources.list.d/kitware.list \
+    && apt-get update && apt-get install -y --no-install-recommends cmake \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /project
+
+# MXE Repository einrichten (focal = Ubuntu 20.04)
 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" \
+        | gpg --dearmor -o /usr/share/keyrings/mxeapt.gpg \
+    && echo "deb [arch=amd64 signed-by=/usr/share/keyrings/mxeapt.gpg] 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.
+# MXE-Pakete: OpenCV + LibRaw (statisch, x86_64)
+# Hinweis: MXE unterstützt kein Qt6 → Windows-Build als CLI ohne GUI
+# Initial-Download ~1-2 GB, dauert je nach Bandbreite 5-15 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-opencv \
     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/*
 
@@ -102,12 +120,13 @@ ENV MXE_PREFIX=/usr/lib/mxe/usr/x86_64-w64-mingw32.static \
 
 COPY . /project
 
+# System-cmake (3.20+) mit MXE-Toolchain und TryRunResults
 RUN cmake -B build-windows -G Ninja \
-        -DCMAKE_TOOLCHAIN_FILE=cmake/toolchain-mingw64.cmake \
+        -DCMAKE_TOOLCHAIN_FILE="${MXE_PREFIX}/share/cmake/mxe-conf.cmake" \
+        -C /usr/lib/mxe/usr/share/cmake/modules/TryRunResults.cmake \
         -DCMAKE_BUILD_TYPE=Release \
-        -DCMAKE_PREFIX_PATH="${MXE_PREFIX}" \
         -DCMAKE_INSTALL_PREFIX=/project/dist-windows \
-        -DBUILD_GUI=ON \
+        -DBUILD_GUI=OFF \
         -DBUILD_TESTS=OFF \
     && cmake --build build-windows --parallel "$(nproc)" \
     && cmake --install build-windows