feat(auth): add places api key management

[salmonumbrella]

Summary

• Add gog auth places-key commands (set/status/clear) for managing Google Places API key
• Support multiple storage backends: keychain (recommended), config file, or environment variable
• Integrate Places API with calendar commands via --location-search and --place-id flags
• Add Places API key management to gog auth manage web UI

Closes #138

Test Plan

• Unit tests for internal/places/apikey.go (MaskAPIKey, empty key validation)
• Integration tests for auth places-key commands
• Integration tests for calendar create/update with Places flags
• All existing tests pass

🤖 Generated with Claude Code

[steipete]

Thanks @salmonumbrella. I reviewed this against the current Places API (New) docs and landed a smaller replacement on main in f550ae5, with final CI/lint cleanup through 57080af.

The original branch was stale/conflicting, so I did not merge it directly. The landed version adds direct Places Text Search / Place Details support without a new dependency, plus calendar create/update --location-search and --place-id. One important API detail: Google Calendar events only expose a free-form location string here, not a writable Calendar place-id field, so gog stores the resolved gog.place_id and gog.place_maps_uri in private extended properties.

Live proof: resolved “Elysian Coffee Vancouver” with Places API and dry-ran a Calendar create showing the canonical location plus private place metadata. Docs/README/generated command docs/changelog updated. CI is green on main: 25601394551. Closing this PR as replaced by the landed implementation.