chore: sane ignore files, update summary, bump base images

- Add .claude/ to .gitignore and untrack settings.local.json
- Create .dockerignore to exclude docs, extension, analysis, scripts,
  node_modules, and other noise from the Docker build context
- Dockerfile: Node 20→22-alpine, Python 3.11→3.13-slim, DEBIAN_FRONTEND
  set, pip upgrade before install
- Track frontend/package-lock.json for reproducible builds
- Update summary.md: date, db.py in project structure, superseded column
  in schema, two new key patterns (12/13), full 2026-03-19 changelog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,60 @@
+# Version control
+.git/
+.gitignore
+.dockerignore
+
+# Claude Code
+.claude/
+
+# Documentation and specs
+docs/
+*.md
+README.md
+
+# Analysis artifacts
+analysis/
+
+# Extension packages
+*.xpi
+extension-dist/
+extension/
+
+# Utility scripts
+scripts/
+
+# Environment files (secrets must be injected via env vars, not baked in)
+.env
+.env.*
+
+# Docker compose files (not needed inside the image)
+docker-compose*.yml
+
+# Runtime data (mounted as volumes)
+data/
+config/
+logs/
+downloads/
+cookies/
+
+# Frontend build intermediates
+frontend/node_modules/
+frontend/dist/
+
+# Python cache and test artifacts
+**/__pycache__/
+**/*.py[cod]
+**/*.egg-info/
+**/.pytest_cache/
+**/.mypy_cache/
+**/.ruff_cache/
+**/.coverage
+**/htmlcov/
+
+# Node dev artifacts
+**/npm-debug.log*
+**/yarn-debug.log*
+**/yarn-error.log*
+
+# OS artifacts
+.DS_Store
+Thumbs.db