feat: extend CliRunner with config file/batch mode and add comprehensive tests

CliRunner:
- --batch / --config <file> flags trigger batch mode with directory scanning
- collect_files() with recursive support and case-insensitive extension matching
- build_pipeline() respects AppConfig conversion flags (invert toggle)
- Progress output to stderr: "[1/42] Processing DSC09246.ARW..."

Tests (test_pipeline.cpp):
- AppConfig: load/save roundtrip, missing file error, extension parsing,
  format mapping, write_default
- CropProcessor: levels adjustment, sharpening no-clip, empty image error
- ColorCorrector: AWB preserves neutral grey, skips B&W film
- Inverter: color negative changes values, B&W inversion, positive passthrough
- Preprocessor: 8-bit→16-bit conversion

test_rawloader.cpp: added missing <fstream> include

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

tests/test_rawloader.cpp

@@ -3,6 +3,7 @@
 #include "converter/rawloader/RawLoader.h"
 
 #include <filesystem>
+#include <fstream>
 
 using namespace photoconv;
 
@@ -28,7 +29,7 @@ TEST(RawLoaderTest, RejectsUnsupportedFormat) {
     // Create a temporary file with unsupported extension
     auto temp = std::filesystem::temp_directory_path() / "test.xyz";
     {
-        std::ofstream f(temp);
+        std::ofstream f{temp};
         f << "dummy";
     }