feat(gui): add auth core, setup gate, and first-run operator creation

- Add migrations 007-010 for system config, operators, sessions, audit_log
- Implement argon2id password hashing via argon2-cffi
- Implement session-based authentication with database-stored tokens
- Add SetupGateMiddleware to redirect to /setup until first operator created
- Add SessionMiddleware to load session from cookie and attach operator
- Create /setup, /login, /logout, /change-password routes with CSRF protection
- Add periodic session cleanup task (hourly)
- Add audit logging for auth events
- Update systemd unit with EnvironmentFile for /etc/central/central.env
- Add comprehensive tests for auth, middleware, and audit modules

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pyproject.toml

@@ -12,9 +12,11 @@ license = {text = "MIT"}
 authors = [{name = "Matt Johnson"}]
 dependencies = [
     "aiohttp>=3.13.5",
+    "argon2-cffi>=25.1.0",
     "asyncpg>=0.31.0",
     "cloudevents>=2.0.0",
     "cryptography>=44.0.0",
+    "fastapi-csrf-protect>=0.4.0",
     "fastapi>=0.115.0",
     "jinja2>=3.1.6",
     "nats-py>=2.14.0",