refactor(schedule): extract application/ layer (stage 5)

- Move service.py -> application/service.py (SchedulerService class name
  unchanged; build_object_store / build_storage_http_client move along)
- main.py imports schedule.application.service
- Rewrite worker.py's lazy `from schedule.service import build_object_store`
  and test_worker.py's mock patch string targets — same class of bug as the
  test_janitor patch strings (silent no-op until the old file is deleted)
- Delete flat service.py (orphaned; only docstring refs remain in
  orchestrator, cleaned up in stage 6)
- Zero behavior change; schedule/pyproject.toml untouched

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

schedule/src/schedule/execution/worker.py

@@ -87,7 +87,7 @@ class NodeExecutor:
         store = self._bucket_stores.get(bucket_name)
         if store is not None:
             return store
-        from schedule.service import build_object_store
+        from schedule.application.service import build_object_store
 
         store = build_object_store(bucket_name=bucket_name)
         self._bucket_stores[bucket_name] = store

schedule/src/schedule/main.py

@@ -9,7 +9,7 @@ from common.db import create_database_engine, create_session_factory
 from common.service_app import create_service_app
 from loguru import logger
 
-from schedule.service import (
+from schedule.application.service import (
     SchedulerService,
     build_object_store,
     build_storage_http_client,

schedule/src/schedule/worker.py

@@ -87,7 +87,7 @@ class NodeExecutor:
         store = self._bucket_stores.get(bucket_name)
         if store is not None:
             return store
-        from schedule.service import build_object_store
+        from schedule.application.service import build_object_store
 
         store = build_object_store(bucket_name=bucket_name)
         self._bucket_stores[bucket_name] = store