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

.env.example

@@ -135,6 +135,15 @@ PATH_DEBUG=false
 # Suppress TVDB API warnings (true/false) - TVDB failures are common and non-critical
 SUPPRESS_TVDB_WARNINGS=true
 
+# ===========================================
+# WEB INTERFACE AUTHENTICATION
+# ===========================================
+# Enable web interface authentication (default: false)
+WEB_AUTH_ENABLED=false
+
+# Session timeout in seconds (default: 3600 = 1 hour)
+WEB_AUTH_SESSION_TIMEOUT=3600
+
 # ===========================================
 # SERVER CONFIGURATION
 # ===========================================