feat: add async AI description generation on file upload

Adds _generate_ai_description background task that fires after a
successful upload: images get a one-sentence vision description via
Claude, text/log/config files get extracted_content + AI summary when
>2000 chars. Runs as asyncio.create_task so it never blocks the upload
response. Errors are logged and swallowed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/endpoints/uploads.py

@@ -35,6 +35,60 @@ def _check_storage_configured() -> None:
         )
 
 
+async def _generate_ai_description(upload_id: UUID, file_data: bytes, content_type: str) -> None:
+    """Background task: generate AI description for uploaded file."""
+    try:
+        from app.core.database import async_session_maker
+        from app.services.assistant_chat_service import _call_ai
+        import base64
+
+        async with async_session_maker() as db:
+            result = await db.execute(
+                select(FileUpload).where(FileUpload.id == upload_id)
+            )
+            upload = result.scalar_one_or_none()
+            if not upload:
+                return
+
+            if content_type.startswith("image/"):
+                b64_data = base64.b64encode(file_data).decode("utf-8")
+                description, _, _ = await _call_ai(
+                    system_base="You are a technical image analyst for IT troubleshooting.",
+                    rag_context="",
+                    history=[],
+                    new_message="Describe this image in one sentence for a troubleshooting context log.",
+                    images=[{"media_type": content_type, "data": b64_data}],
+                    max_tokens=100,
+                )
+                upload.ai_description = description
+            elif content_type.startswith("text/") or content_type in (
+                "application/json", "application/xml", "application/yaml",
+            ):
+                try:
+                    text_content = file_data.decode("utf-8")
+                except UnicodeDecodeError:
+                    text_content = file_data.decode("latin-1")
+
+                upload.extracted_content = text_content[:10000]
+
+                if len(text_content) > 2000:
+                    summary, _, _ = await _call_ai(
+                        system_base="You are a technical log/config analyst.",
+                        rag_context="",
+                        history=[],
+                        new_message=f"Summarize this file content in 2-3 sentences:\n\n{text_content[:5000]}",
+                        max_tokens=200,
+                    )
+                    upload.content_summary = summary
+                    upload.ai_description = summary
+                else:
+                    upload.ai_description = f"Text file: {upload.filename}"
+
+            await db.commit()
+    except Exception:
+        logger.exception(f"Failed to generate AI description for upload {upload_id}")
+
+
 @router.post("", response_model=FileUploadResponse, status_code=status.HTTP_201_CREATED)
 @limiter.limit("10/minute")
 async def upload_file(
@@ -113,6 +167,11 @@ async def upload_file(
     await db.commit()
     await db.refresh(upload)
 
+    import asyncio
+    asyncio.create_task(
+        _generate_ai_description(upload.id, file_data, content_type)
+    )
+
     presigned_url = storage_service.get_presigned_url(upload.storage_key)
 
     return FileUploadResponse(