v2.0: dual deployment — pip install (SQLite) + Docker (PostgreSQL)

Architecture:
- Moved backend/app/ to diligence/ Python package
- Dialect-agnostic models (Uuid + JSON, no PostgreSQL imports)
- Auto-detect database: empty DATABASE_URL → SQLite at ~/.diligence/data.db
- Cross-dialect migrations (inspector-based, no raw PostgreSQL DDL)
- FastAPI serves pre-built React frontend for pip path
- CLI entry point: diligence [--port] [--no-browser] [--data-dir]
- pyproject.toml with optional deps: [postgres], [mcp], [dev]
- Docker path unchanged: docker compose up -d

pip install path: pip install . && diligence
Docker path: ./setup.sh && docker compose up -d

.gitignore

@@ -1,12 +1,31 @@
+# Environment
+.env
+*.env.local
+
+# Python
 __pycache__/
 *.py[cod]
 *.egg-info/
-.env
-.venv/
-node_modules/
 dist/
-.DS_Store
-*.log
+build/
+*.egg
 
-# Excluded from open-source (scraped third-party content)
+# Node
+frontend/node_modules/
+frontend/dist/
+
+# Data
+*.db
+*.sqlite
+*.sqlite3
+
+# IDE
+.vscode/
+.idea/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Content (scraped recipes — not for distribution)
 content/