feat(AU): add Central Coast (NSW LGA) city entry (#1521)

Adds the Central Coast Council LGA — the regional designation covering
~340k residents in NSW between Sydney and Newcastle, formed by 2016 merger
of Gosford City Council and Wyong Shire Council.

Constituent suburbs (Gosford, Wyong, Erina, Terrigal, etc.) already exist
as separate 'section' rows. This entry serves as the LGA-level identifier
for users querying the region directly.

Closes #1521.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dr5hn

contributions/cities/AU.json

@@ -169984,5 +169984,20 @@
     "updated_at": "2025-12-02T16:59:27",
     "flag": 1,
     "wikiDataId": "Q3135649"
+  },
+  {
+    "name": "Central Coast",
+    "state_id": 3909,
+    "state_code": "NSW",
+    "country_id": 14,
+    "country_code": "AU",
+    "type": "city",
+    "latitude": "-33.30000000",
+    "longitude": "151.35000000",
+    "timezone": "Australia/Sydney",
+    "wikiDataId": "Q5061498",
+    "id": 160614,
+    "created_at": "2026-05-06T18:41:28",
+    "updated_at": "2026-05-06T18:41:28"
   }
 ]