refactor: solidify startup UX and engine-aware preprocessing

- Slim core deps: move ML stack to optional extras (paddle/tables/figures/scientific/full)
- Lazy settings proxy with config search paths (env var, cwd, user dir)
- New commands: init, demo, setup [basic|full], first-run guard on run/watch
- Engine-aware preprocessing: Paddle gets original image (fixes dark mode 0.83->0.95)
- Results table shows Skipped count; lazy run-dir creation
- kg_ocr marked experimental with extra, Docker defaults with OCR_PIPELINE_CONFIG
- 25/25 tests, ruff clean

tests/test_postprocess.py

@@ -1,9 +1,8 @@
 import pytest
-from pathlib import Path
 
-from ocr_pipeline.postprocess.clean import clean_text, CleanResult
-from ocr_pipeline.postprocess.chunk import chunk_text, TextChunk
 from ocr_pipeline.config import settings
+from ocr_pipeline.postprocess.chunk import TextChunk, chunk_text
+from ocr_pipeline.postprocess.clean import clean_text
 
 
 class TestTextCleaning:
@@ -70,4 +69,4 @@ class TestConfig:
 
 
 if __name__ == "__main__":
-    pytest.main([__file__, "-v"])
+    pytest.main([__file__, "-v"])