Add Video Learning Agent for short video platforms

Features:
- VideoLearningAgent for automated video watching on Douyin/Kuaishou/TikTok
- Web dashboard UI for video learning sessions
- Real-time progress tracking with screenshot capture
- App detection using get_current_app() for accurate recording
- Session management with pause/resume/stop controls

Technical improvements:
- Simplified video detection logic using direct app detection
- Full base64 hash for sensitive screenshot change detection
- Immediate stop when target video count is reached
- Fixed circular import issues with ModelConfig

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

dashboard/static/index.html

@@ -41,6 +41,13 @@
                 </div>
             </div>
             <div class="header-actions">
+                <a href="/static/video-learning.html" class="btn btn-primary">
+                    <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+                        <polygon points="23 7 16 12 23 17 23 7"></polygon>
+                        <rect x="1" y="5" width="15" height="14" rx="2" ry="2"></rect>
+                    </svg>
+                    Video Learning
+                </a>
                 <button @click="refreshDevices" class="btn btn-secondary" :disabled="refreshing">
                     <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" :class="{ spinning: refreshing }">
                         <polyline points="23 4 23 10 17 10"></polyline>