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>
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