refactor: clean up WordPress URL validation with centralized error handling

- Replace 11 repetitive try-catch blocks with two reusable wrapper functions
- Add wordpressFetchGraceful for functions that should return fallbacks
- Add wordpressFetchPaginatedGraceful for paginated queries
- Single isConfigured check instead of multiple !baseUrl validations
- Extract USER_AGENT and CACHE_TTL constants
- Reduce file from 491 to 438 lines (-53 lines, cleaner code)

Author: claude