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/conftest.py

@@ -1,4 +1,4 @@
 import sys
 from pathlib import Path
 
-sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
+sys.path.insert(0, str(Path(__file__).parent.parent / "src"))