feat: implement user authentication module

- Backend (FastAPI):
  - External API authentication (pj-auth-api.vercel.app)
  - JWT token validation with Redis session storage
  - RBAC with department isolation
  - User, Role, Department models with pjctrl_ prefix
  - Alembic migrations with project-specific version table
  - Complete test coverage (13 tests)

- Frontend (React + Vite):
  - AuthContext for state management
  - Login page with error handling
  - Protected route component
  - Dashboard with user info display

- OpenSpec:
  - 7 capability specs defined
  - add-user-auth change archived

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/.gitignore

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+# Dependencies
+node_modules/
+
+# Build output
+dist/
+build/
+
+# Environment
+.env
+*.env.local
+
+# IDE
+.vscode/
+.idea/
+
+# OS
+.DS_Store
+
+# Logs
+*.log
+npm-debug.log*
+
+# Cache
+.cache/