chore: initial project setup

Phase 0 — full project scaffold with:
- Backend: FastAPI + SQLAlchemy 2.0 async + Alembic + PostgreSQL 16
- Frontend: React 18 + TypeScript + Vite + Tailwind CSS + shadcn/ui
- Docker Compose (prod + dev override with hot-reload)
- Health endpoint, CORS config, API proxy, env template

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

docker-compose.override.yml

@@ -0,0 +1,25 @@
+services:
+  backend:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile
+    command: uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload
+    volumes:
+      - ./backend:/app
+    environment:
+      DEBUG: "true"
+
+  frontend:
+    image: node:20-alpine
+    working_dir: /app
+    command: sh -c "npm install && npm run dev -- --host 0.0.0.0"
+    volumes:
+      - ./frontend:/app
+      - frontend_node_modules:/app/node_modules
+    ports:
+      - "5173:5173"
+    environment:
+      NODE_ENV: development
+
+volumes:
+  frontend_node_modules: