Improve opportunity location search and deadline defaults

[johnsutor]

Summary

• replace the inconsistent opportunity location facet menu with location-aware text search
• store Nominatim city, state, postal code, and country components for Meilisearch
• keep unsearched browsing on Open Now, but default text searches to All Opportunities
• add the All Opportunities deadline option and sort that view alphabetically
• add localized search guidance and OpenStreetMap attribution

Validation

• corepack pnpm lint
• corepack pnpm test:unit (53 files, 728 tests)
• corepack pnpm build
• desktop and mobile browser checks on /opportunities

Deployment note

The production opportunities index settings were applied and 396 documents were reindexed. The next scraper run after merge will populate the new structured location fields in Firestore.