fix: resolve ruff lint and formatting issues

Remove unused timedelta import from test_wireless_api.py and
auto-format metrics.py to pass ruff format check.

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

backend/app/routers/metrics.py

@@ -480,7 +480,8 @@ async def get_wireless_issues(
         else:
             issue = "Degraded"
 
-        issues.append({
+        issues.append(
+            {
                 "device_id": str(row.device_id),
                 "hostname": row.hostname,
                 "interface": row.interface,
@@ -489,7 +490,8 @@ async def get_wireless_issues(
                 "ccq": row.ccq,
                 "client_count": row.client_count,
                 "frequency": row.frequency,
-        })
+            }
+        )
 
     return issues
 
@@ -556,7 +558,8 @@ async def get_fleet_wireless_issues(
         else:
             issue = "Degraded"
 
-        issues.append({
+        issues.append(
+            {
                 "device_id": str(row.device_id),
                 "hostname": row.hostname,
                 "tenant_name": row.tenant_name,
@@ -566,6 +569,7 @@ async def get_fleet_wireless_issues(
                 "ccq": row.ccq,
                 "client_count": row.client_count,
                 "frequency": row.frequency,
-        })
+            }
+        )
 
     return issues

backend/tests/integration/test_wireless_api.py

@@ -9,7 +9,7 @@ All tests run against real PostgreSQL+TimescaleDB.
 """
 
 import uuid
-from datetime import datetime, timedelta, timezone
+from datetime import datetime, timezone
 
 import pytest
 from sqlalchemy import text