feat: implement 5 QA-driven security and quality proposals

Implemented proposals from comprehensive QA review:

1. extend-csrf-protection
   - Add POST to CSRF protected methods in frontend
   - Global CSRF middleware for all state-changing operations
   - Update tests with CSRF token fixtures

2. tighten-cors-websocket-security
   - Replace wildcard CORS with explicit method/header lists
   - Disable query parameter auth in production (code 4002)
   - Add per-user WebSocket connection limit (max 5, code 4005)

3. shorten-jwt-expiry
   - Reduce JWT expiry from 7 days to 60 minutes
   - Add refresh token support with 7-day expiry
   - Implement token rotation on refresh
   - Frontend auto-refresh when token near expiry (<5 min)

4. fix-frontend-quality
   - Add React.lazy() code splitting for all pages
   - Fix useCallback dependency arrays (Dashboard, Comments)
   - Add localStorage data validation in AuthContext
   - Complete i18n for AttachmentUpload component

5. enhance-backend-validation
   - Add SecurityAuditMiddleware for access denied logging
   - Add ErrorSanitizerMiddleware for production error messages
   - Protect /health/detailed with admin authentication
   - Add input length validation (comment 5000, desc 10000)

All 521 backend tests passing. Frontend builds successfully.

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

backend/app/core/config.py

@@ -28,7 +28,8 @@ class Settings(BaseSettings):
     # JWT - Must be set in environment, no default allowed
     JWT_SECRET_KEY: str = ""
     JWT_ALGORITHM: str = "HS256"
-    JWT_EXPIRE_MINUTES: int = 10080  # 7 days
+    JWT_EXPIRE_MINUTES: int = 60  # 1 hour (short-lived access token)
+    REFRESH_TOKEN_EXPIRE_DAYS: int = 7  # Refresh token valid for 7 days
 
     @field_validator("JWT_SECRET_KEY")
     @classmethod
@@ -127,6 +128,12 @@ class Settings(BaseSettings):
     QUERY_LOGGING: bool = False  # Enable SQLAlchemy query logging
     QUERY_COUNT_THRESHOLD: int = 10  # Warn when query count exceeds this threshold
 
+    # Environment
+    ENVIRONMENT: str = "development"  # Options: development, staging, production
+
+    # WebSocket Settings
+    MAX_WEBSOCKET_CONNECTIONS_PER_USER: int = 5  # Maximum concurrent WebSocket connections per user
+
     class Config:
         env_file = ".env"
         case_sensitive = True