YachtMemory AnchorageGeocoder - Overpass Retry V1

Change scope:
- No decision-rule changes.
- No query, bbox, cache schema or acquisition-policy changes.
- Adds same-endpoint retry/backoff only for transient Overpass failures:
  HTTP 429, 502, 503, 504 and transport failure.
- Maximum 3 attempts per endpoint.
- Backoff: 2 seconds, then 5 seconds.
- Non-transient errors immediately fall through to the next endpoint.
- Database behavior unchanged; AnchorageGeocoder remains DB read-only.

Target:
  /var/www/app.yachtmemory.net/src/services/AnchorageGeocoder.php
