Implement complete user authentication system

- Configured Flask-Login with user_loader
- Added register, login, logout routes with proper validation
- Created login.html and register.html templates with auth forms
- Updated base.html navigation to show username and conditional menu
- Added auth page styling to style.css
- Protected all routes with @login_required decorator
- Updated all routes to filter by current_user.id
- Added user ownership validation for:
  - Channels (can only view/refresh own channels)
  - Videos (can only watch/download own videos)
  - Streams (can only stream videos from own channels)
- Updated save_to_db() calls to pass current_user.id
- Improved user_loader to properly handle session management

Features:
- User registration with password confirmation
- Secure password hashing with bcrypt
- Login with "remember me" functionality
- Flash messages for all auth actions
- Redirect to requested page after login
- User-specific data isolation (multi-tenant)

Security:
- All sensitive routes require authentication
- Users can only access their own data
- Passwords hashed with bcrypt salt
- Session-based authentication via Flask-Login

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

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

templates/base.html

@@ -11,9 +11,18 @@
         <div class="nav-container">
             <h1 class="logo"><a href="/">YottoB</a></h1>
             <ul class="nav-menu">
-                <li><a href="/" class="{% if request.path == '/' %}active{% endif %}">Videos</a></li>
-                <li><a href="/channels" class="{% if request.path == '/channels' %}active{% endif %}">Channels</a></li>
-                <li><a href="/add-channel" class="{% if request.path == '/add-channel' %}active{% endif %}">Add Channel</a></li>
+                {% if current_user.is_authenticated %}
+                    <li><a href="/" class="{% if request.path == '/' %}active{% endif %}">Videos</a></li>
+                    <li><a href="/channels" class="{% if request.path == '/channels' %}active{% endif %}">Channels</a></li>
+                    <li><a href="/add-channel" class="{% if request.path == '/add-channel' %}active{% endif %}">Add Channel</a></li>
+                    <li class="nav-user">
+                        <span>{{ current_user.username }}</span>
+                        <a href="{{ url_for('logout') }}">Logout</a>
+                    </li>
+                {% else %}
+                    <li><a href="{{ url_for('login') }}" class="{% if request.path == '/login' %}active{% endif %}">Login</a></li>
+                    <li><a href="{{ url_for('register') }}" class="{% if request.path == '/register' %}active{% endif %}">Register</a></li>
+                {% endif %}
             </ul>
         </div>
     </nav>