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/main.cpp

@@ -0,0 +1,54 @@
+#include "cli/CliRunner.h"
+#include "gui/MainWindow.h"
+
+#include <QApplication>
+
+#include <algorithm>
+#include <iostream>
+#include <string>
+
+/**
+ * @brief Application entry point.
+ *
+ * Supports two modes:
+ * - GUI mode (default): launches the Qt MainWindow
+ * - CLI mode (--cli flag): batch processes files without GUI
+ */
+int main(int argc, char* argv[]) {
+    // Check if CLI mode is requested
+    bool cli_mode = false;
+    for (int i = 1; i < argc; ++i) {
+        if (std::string{argv[i]} == "--cli") {
+            cli_mode = true;
+            break;
+        }
+    }
+
+    if (cli_mode) {
+        // CLI batch mode (no Qt dependency)
+        auto config_result = photoconv::CliRunner::parse_args(argc, argv);
+        if (!config_result.has_value()) {
+            std::cerr << config_result.error().format() << std::endl;
+            return 1;
+        }
+
+        photoconv::CliRunner runner;
+        auto result = runner.run(config_result.value());
+        if (!result.has_value()) {
+            std::cerr << result.error().format() << std::endl;
+            return 1;
+        }
+
+        return result.value() > 0 ? 0 : 1;
+    }
+
+    // GUI mode
+    QApplication app(argc, argv);
+    app.setApplicationName("Photo Converter");
+    app.setApplicationVersion("0.1.0");
+
+    photoconv::MainWindow window;
+    window.show();
+
+    return app.exec();
+}