feat: add background tasks monitoring dashboard

Adds a unified view of all background tasks (imports and test runs)
under Platform Monitoring. Includes real-time status polling,
statistics overview, and task history.

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

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

app/routes/admin_pages.py

@@ -500,6 +500,25 @@ async def admin_imports_page(
     )
 
 
+@router.get("/background-tasks", response_class=HTMLResponse, include_in_schema=False)
+async def admin_background_tasks_page(
+    request: Request,
+    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    db: Session = Depends(get_db),
+):
+    """
+    Render background tasks monitoring page.
+    Shows running and completed background tasks across the system.
+    """
+    return templates.TemplateResponse(
+        "admin/background-tasks.html",
+        {
+            "request": request,
+            "user": current_user,
+        },
+    )
+
+
 @router.get("/marketplace", response_class=HTMLResponse, include_in_schema=False)
 async def admin_marketplace_page(
     request: Request,