Add test user seed, password validation, and pre-commit security hook

- backend/scripts/seed.py: creates test@example.com on dev startup
- backend/scripts/start_dev.sh: runs migrations + seed + uvicorn --reload
- backend/app/schemas/user.py: password validator (length, case, digit, special char, forbidden words)
- scripts/security_check.py: Docker-based scanner for secrets, dangerous patterns, weak crypto, bandit
- .githooks/pre-commit: runs security_check.py in python:3.12-slim on every commit

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

docker-compose.dev.yml

@@ -4,7 +4,7 @@
 services:
 
   backend:
-    command: uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload
+    command: sh scripts/start_dev.sh
     volumes:
       - ./backend:/app