Scaffold Reverso MVP pipeline structure

Set up the project skeleton per PLAN.md §4:
- src/ package: identifiers, disease, drugs, scoring, provenance
  with pydantic schemas and confidence-tier logic (working);
  data-pull/compute functions stubbed per their build week
- 5 starter notebooks (01-05) with PLAN-referenced steps
- tests/test_scoring.py: tier-assignment tests pass; scoring
  reference test xfail until Week 3
- docs/: recovery_test_report, data_sources, known_limitations skeletons
- pyproject.toml (requires-python >=3.11,<3.14), .gitignore, README
- data/ tree preserved via .gitkeep; raw/processed/results gitignored

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,33 @@
+# Data — never commit raw or processed data; keep directory structure via .gitkeep.
+# Re-include directories first (!data/**/), else .gitkeep inside an excluded dir
+# cannot be un-ignored.
+data/raw/**
+data/processed/**
+data/results/**
+!data/**/
+!data/**/.gitkeep
+
+# Python
+__pycache__/
+*.py[cod]
+*.egg-info/
+.eggs/
+build/
+dist/
+.venv/
+venv/
+env/
+
+# Jupyter
+.ipynb_checkpoints/
+*/.ipynb_checkpoints/
+
+# Tooling caches
+.pytest_cache/
+.ruff_cache/
+.mypy_cache/
+
+# OS / editor
+.DS_Store
+.idea/
+.vscode/