fix(tags): move _NORMALIZE_CHUNK_SECONDS above the decorator (syntax error)

The constant + comment landed BETWEEN @celery.task(...) and the function def,
which is a syntax error that broke the whole tasks.admin import (cascaded to
lint E999 + every backend/integration test). Move it above the decorator.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/tasks/admin.py

@@ -75,13 +75,6 @@ def reextract_archive_attachments_task(self) -> dict:
         )
 
 
-@celery.task(
-    name="backend.app.tasks.admin.normalize_tags_task",
-    bind=True,
-    autoretry_for=(OperationalError, DBAPIError),
-    retry_backoff=15, retry_backoff_max=180, max_retries=1,
-    soft_time_limit=1800, time_limit=2400,  # 30 min / 40 min
-)
 # Time-box one chunk well under the soft limit so a large back-catalog (the
 # first run recases the whole booru vocabulary) can't run the task into the
 # Celery time limit — it timed out at 40 min, operator-flagged 2026-06-07. The
@@ -91,6 +84,13 @@ def reextract_archive_attachments_task(self) -> dict:
 _NORMALIZE_CHUNK_SECONDS = 600
 
 
+@celery.task(
+    name="backend.app.tasks.admin.normalize_tags_task",
+    bind=True,
+    autoretry_for=(OperationalError, DBAPIError),
+    retry_backoff=15, retry_backoff_max=180, max_retries=1,
+    soft_time_limit=1800, time_limit=2400,  # 30 min / 40 min
+)
 def normalize_tags_task(self) -> dict:
     """Wraps tag_service.normalize_existing_tags (#714): Title-Case the
     back-catalog and merge case/whitespace-variant duplicate tags via the