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

static/index.html

@@ -15,6 +15,14 @@
                 <h1><i class="fas fa-shield-alt"></i> NFOGuard</h1>
                 <p>Database Management & Reporting</p>
             </div>
+            <div class="auth-status" id="auth-status" style="display: none;">
+                <span class="auth-user">
+                    <i class="fas fa-user"></i> <span id="auth-username">Loading...</span>
+                </span>
+                <button class="auth-logout" id="logout-btn" onclick="logout()">
+                    <i class="fas fa-sign-out-alt"></i> Logout
+                </button>
+            </div>
             <nav class="nav-tabs">
                 <button class="nav-tab active" data-tab="dashboard">
                     <i class="fas fa-tachometer-alt"></i> Dashboard