fix(core): centralize async/sync bridge for APScheduler scheduled jobs

Create AsyncJobRunner — centralized bridge between APScheduler
(BackgroundScheduler, sync thread pool) and async coroutines.

Fixes:
- P0: execute_run() called without await from APScheduler thread,
  causing coroutine to be silently discarded (root cause: no
  translation history)
- P0: get_async_job_runner() deadlock when called from APScheduler
  thread pool without running event loop
- P1: ID mismatch in disable_schedule/delete_schedule routes
  (job_id passed instead of schedule_id)
- P1: asyncio.run() in APScheduler callbacks incompatible with
  running event loop
- Delete unused llm_analysis/scheduler.py (not used in production)

Changes:
  core/async_job_runner.py          — new: AsyncJobRunner class
  core/scheduler.py                 — use runner.run()/run_later()
  translate/scheduler.py            — use runner.run() for execute_run
  mapping_service.py                — remove unused BackgroundScheduler
  dependencies.py                   — add get_async_job_runner() DI
  app.py                            — init runner in lifespan
  api/routes/migration.py           — use runner.run()
  _schedule_routes.py               — fix ID mismatch
  plugins/migration.py              — use runner.run()
  llm_analysis/scheduler.py         — delete (unused)
  tests: 151 new/updated tests, all passing

backend/src/api/routes/migration.py

@@ -32,7 +32,7 @@ from ...core.logger import belief_scope, logger
 from ...core.mapping_service import IdMappingService
 from ...core.migration.dry_run_orchestrator import MigrationDryRunService
 from ...core.async_superset_client import AsyncSupersetClient
-from ...dependencies import get_config_manager, get_task_manager, has_permission
+from ...dependencies import get_async_job_runner, get_config_manager, get_task_manager, has_permission
 from ...models.dashboard import DashboardMetadata, DashboardSelection
 from ...models.mapping import ResourceMapping
 
@@ -377,12 +377,13 @@ async def trigger_sync_now(
         db.commit()
 
         service = IdMappingService(db)
+        runner = get_async_job_runner()
         results = {"synced": [], "failed": []}
 
         for env in environments:
             try:
                 client = AsyncSupersetClient(env)
-                service.sync_environment(env.id, client)
+                runner.run(service.sync_environment(env.id, client))
                 results["synced"].append(env.id)
                 logger.reason(f"Synced environment {env.id}", extra={"src": "trigger_sync_now"})
             except Exception as e: