feat: Add optional web interface authentication with session management

Authentication Features:
  - Optional HTTP Basic Auth with session cookies for web interface protection
  - Configurable username/password with session timeout (default: 1 hour)
  - Selective route protection (web interface protected, webhooks/APIs remain public)
  - Authentication status display with logout functionality in web UI
  - Session cleanup and graceful logout with browser re-authentication prompt

  Configuration:
  - WEB_AUTH_ENABLED in .env (default: false - no breaking changes)
  - WEB_AUTH_USERNAME/WEB_AUTH_PASSWORD in .env.secrets
  - WEB_AUTH_SESSION_TIMEOUT configurable (5min-24h range)

  Development Tools:
  - Added debug_tv.py for TV series/episode debugging (series, season, episode levels)
  - Comprehensive episode data inspection with validation and sources breakdown
  - Complements existing debug_movie.py for complete media debugging coverage

  Technical Implementation:
  - SimpleAuthMiddleware with FastAPI integration
  - Session management with automatic cleanup
  - Authentication status API endpoints
  - Responsive CSS styling for auth UI elements
  - JavaScript functions for auth checking and logout

config/settings.py

@@ -79,6 +79,9 @@ class NFOGuardConfig:
         
         # TV processing
         self._load_tv_settings()
+        
+        # Web interface authentication
+        self._load_auth_settings()
     
     def _load_paths(self) -> None:
         """Load and validate path configuration"""
@@ -156,6 +159,13 @@ class NFOGuardConfig:
         self.tv_season_dir_pattern = os.environ.get("TV_SEASON_DIR_PATTERN", "season ").lower()
         self.tv_webhook_processing_mode = os.environ.get("TV_WEBHOOK_PROCESSING_MODE", "targeted").lower()
     
+    def _load_auth_settings(self) -> None:
+        """Load web interface authentication settings"""
+        self.web_auth_enabled = _bool_env("WEB_AUTH_ENABLED", False)
+        self.web_auth_username = os.environ.get("WEB_AUTH_USERNAME", "admin")
+        self.web_auth_password = os.environ.get("WEB_AUTH_PASSWORD", "")
+        self.web_auth_session_timeout = self._get_int_env("WEB_AUTH_SESSION_TIMEOUT", 3600, 300, 86400)  # 1 hour default, 5min-24h range
+    
     def _get_int_env(self, name: str, default: int, min_val: int, max_val: int) -> int:
         """Get integer environment variable with validation"""
         value_str = os.environ.get(name)