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

docker/config.docker.yaml

@@ -0,0 +1,15 @@
+# Container defaults: host directories are mounted under /data.
+# Selected via OCR_PIPELINE_CONFIG in the image.
+input:
+  paths:
+    - "/data/screenshots"
+
+ocr:
+  engine: "tesseract"
+
+output:
+  base_directory: "/data/output"
+  write_consolidated: true
+
+watch:
+  db_path: "/data/output/processed_files.db"