Add screenshot content analysis using VLM

Features:
- ScreenshotAnalyzer class for VLM-based image analysis
- Real-time analysis during video recording
- Extract likes, comments, tags, category from screenshots
- Frontend display for category badges and tags
- Batch analysis API endpoint

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

dashboard/static/video-learning.html

@@ -228,6 +228,12 @@
                                     {{ formatNumber(video.comments) }}
                                 </span>
                             </div>
+                            <div class="video-category" v-if="video.category">
+                                <span class="category-badge">{{ video.category }}</span>
+                            </div>
+                            <div class="video-tags" v-if="video.tags && video.tags.length > 0">
+                                <span class="tag" v-for="tag in video.tags" :key="tag">#{{ tag }}</span>
+                            </div>
                         </div>
                     </div>
                 </div>