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/CMakeLists.txt

@@ -17,6 +17,10 @@ target_include_directories(test_pipeline PRIVATE
     ${CMAKE_SOURCE_DIR}/src
 )
 
+target_compile_definitions(test_pipeline PRIVATE
+    TEST_DATA_DIR="${CMAKE_SOURCE_DIR}/import"
+)
+
 add_test(NAME PipelineTests COMMAND test_pipeline)
 
 # ──────────────────────────────────────────────
@@ -36,12 +40,8 @@ target_include_directories(test_rawloader PRIVATE
     ${CMAKE_SOURCE_DIR}/src
 )
 
-add_test(NAME RawLoaderTests COMMAND test_rawloader)
-
-# Make test data path available
-target_compile_definitions(test_pipeline PRIVATE
-    TEST_DATA_DIR="${CMAKE_SOURCE_DIR}/import"
-)
 target_compile_definitions(test_rawloader PRIVATE
     TEST_DATA_DIR="${CMAKE_SOURCE_DIR}/import"
 )
+
+add_test(NAME RawLoaderTests COMMAND test_rawloader)