chore: initial project scaffold from architecture design

- Add CLAUDE.md with project overview, tech stack, build commands,
  architecture description, coding standards, and sample images section
- Add full directory structure: src/, docs/, tests/, import/
- Add CMakeLists.txt with C++20, OpenCV/LibRaw/Qt6 dependencies,
  converter_core static lib, optional GUI, and GTest tests
- Add architecture documentation: ARCHITECTURE.md, PIPELINE.md, MODULES.md
- Add source skeletons for all pipeline stages:
  RawLoader, Preprocessor, NegativeDetector, Inverter, ColorCorrector,
  CropProcessor, OutputWriter, Pipeline, MainWindow, CliRunner, main.cpp
- Add initial test stubs for pipeline and rawloader
- Add sample ARW files in import/ for integration testing

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

src/converter/pipeline/ImageData.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <opencv2/core.hpp>
+
+#include <cstdint>
+#include <optional>
+#include <string>
+
+namespace photoconv {
+
+/**
+ * @brief Film type classification for processing decisions.
+ */
+enum class FilmType {
+    Unknown,
+    ColorNegative,   // C-41 process
+    BWNegative,      // B&W negative
+    ColorPositive,   // Slide / E-6
+    BWPositive,      // B&W positive
+};
+
+/**
+ * @brief RAW metadata extracted from the image file.
+ *
+ * Populated by the Loader stage and carried through the pipeline
+ * for use by downstream stages (e.g., color correction using WB data).
+ */
+struct RawMetadata {
+    std::string camera_make;       // e.g. "Sony", "Canon", "Nikon"
+    std::string camera_model;      // e.g. "ILCE-7M3"
+    float iso_speed{0.0f};
+    float shutter_speed{0.0f};     // seconds
+    float aperture{0.0f};          // f-number
+    float focal_length{0.0f};      // mm
+    float wb_red{1.0f};            // White balance multipliers
+    float wb_green{1.0f};
+    float wb_blue{1.0f};
+    int raw_width{0};
+    int raw_height{0};
+    int raw_bit_depth{0};          // Bits per channel in source
+    std::string timestamp;         // ISO 8601
+};
+
+/**
+ * @brief Core data structure flowing through the entire pipeline.
+ *
+ * Every pipeline stage receives an ImageData, transforms it, and
+ * returns a new ImageData (or Error) via std::expected.
+ *
+ * Invariants:
+ * - rgb is always CV_16UC3 (16-bit, 3-channel BGR)
+ * - metadata is populated after the Loader stage
+ * - film_type is set after the Detect stage
+ */
+struct ImageData {
+    cv::Mat rgb;                              // 16-bit BGR (CV_16UC3)
+    std::string source_path;                  // Original file path
+    RawMetadata metadata;                     // Camera/RAW metadata
+    FilmType film_type{FilmType::Unknown};    // Detected after Detect stage
+    std::optional<cv::Rect> crop_region;      // Set by Crop stage
+};
+
+} // namespace photoconv