feat: enhance video generation responses with database ID and update dashboard to display pending and completed videos

Co-authored-by: Copilot <copilot@github.com>

backend/app/models/ai.py

@@ -91,7 +91,8 @@ class VideoFromImageRequest(BaseModel):
 
 
 class VideoResponse(BaseModel):
-    id: str
+    id: str  # This is the job_id from the provider
+    db_id: str | None = None  # This is the UUID from our generated_videos table
     model: str
     status: str  # "queued" | "processing" | "completed" | "failed"
     polling_url: str | None = None