feat: production docker + documentation

- Backend Dockerfile: multi-stage build with venv, gunicorn+uvicorn workers, entrypoint runs alembic then gunicorn
- Frontend Dockerfile: multi-stage with npm ci, nginx:1.27-alpine runtime
- nginx.conf: gzip compression, security headers (X-Frame-Options, X-Content-Type-Options, etc.), static asset caching, correct API proxy preserving /api/ prefix
- docker-compose.yml: production config — db healthcheck, backend healthcheck, frontend depends_on backend healthy, no exposed backend port
- docker-compose.override.yml: dev hot-reload — uvicorn --reload with source mount, npm run dev on port 5173
- Rate limiting: slowapi middleware on /auth/login (10/min) and /auth/register (5/min)
- README.md: full documentation with architecture, quick start, API table, dev/prod instructions, tests
- .env.example: all variables documented with comments
- .gitignore: extended with *.pyc, *.cover, .ruff_cache, frontend/.vite, etc.

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

backend/entrypoint.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+set -e
+
+echo "Running database migrations..."
+alembic upgrade head
+
+echo "Starting server..."
+exec gunicorn app.main:app \
+    --workers 4 \
+    --worker-class uvicorn.workers.UvicornWorker \
+    --bind 0.0.0.0:8000 \
+    --timeout 120 \
+    --access-logfile - \
+    --error-logfile -