## Changes
### Server
- Expand LOCATION_MAP to support city/country-level locations for the
15-location tier (US East/West, Toronto, London, Frankfurt, Amsterdam,
Warsaw, Tokyo, Singapore, Mumbai, Sydney, Brazil, Santiago, Johannesburg,
Dubai)
- Add globalpingLocationsTier field to Settings type, Mongoose model,
repository mapper, and Joi validation (valid: 3, 6, 15, default: 6)
- Update getGlobalpingLocations endpoint to return locations based on
the configured tier from settings
- Pass settingsService to MonitorController for tier lookup
### Client
- Add tier selector (radio buttons) to SettingsGlobalping component
with descriptions for each option:
- 3 locations: North America, Europe, Asia
- 6 locations: all continents
- 15 locations: city-level global coverage
- Add rate limits info box explaining credit usage per tier:
- Without token: 250 tests/hour
- With free token: 500 tests/hour
- GitHub sponsors: higher limits
- Add all translation keys for tier labels, descriptions, and rate info
## Benefits
- Admins can choose the right balance of coverage vs API usage
- Rate limit info helps users decide whether they need authentication