feat: add Philippine postal code lookups

[aivangogh]

Summary

• bundle the GeoNames Philippine postal-code snapshot with attribution
• add lazy postal-code lookups by ZIP code and PSGC municipality
• resolve reviewed historical naming differences and cover all 1,656 current municipalities/cities
• inherit PHLPost postal areas for the eight BARMM SGA municipalities
• document the API and verify packed-package/browser exports

Verification

• pnpm build
• pnpm typecheck
• pnpm exec vitest run --dir tests (74 tests)
• pnpm test:browser
• git diff --check