Add Trip Editor geocode search

[stef-k]

Summary

• Added authenticated Trip Editor geocode search proxy.
• Added Nominatim provider behind backend abstraction.
• Browser calls only same-origin /api/trips/{tripId}/editor/geocode/search.
• Added app-wide rate limiting, short cache, deterministic provider status mapping, attribution, User-Agent/Referer handling, and caller cancellation propagation.
• Removed fake geocode contact identity; default geocode User-Agent is plain Wayfarer/1.0, configured TripEditorGeocode:NominatimUserAgent wins.
• Updated shadow search-add targeting so shadow/unassigned region is not targetable.
• Added map search UI with explicit Search/Enter trigger, no request on typing, abort/stale-response handling, result states, preview marker, and cleanup.
• Added search-add draft workflow using explicit normal-region selector and existing Add Place draft path.
• Add as place populates name/address/location, keeps default icon/color, sets reverseGeocode false, and does not save until Save Place.

Closes #262

Scope exclusions

• no browser-direct Nominatim/external provider calls
• no reverse-geocode save behavior changes
• no unrelated area/place/segment behavior changes
• no marker drag
• no final cutover
• no legacy behavior changes
• no mobile/API token contract changes

Validation

• in-flight Search blocker fixed in ec7d59e
• latest GitHub checks passed
• dotnet build passed, existing ASP0000 warning only
• dotnet test tests/Wayfarer.Tests/Wayfarer.Tests.csproj --filter TripEditor passed, 158 tests
• full dotnet test passed earlier in branch, 1588 tests
• npm run build passed
• npx playwright test --config=playwright.config.ts --list passed, 57 tests listed
• focused map-search Playwright spec passed earlier in branch, 8/8
• full npm run test:e2e:trip-editor passed earlier in branch, 56 passed / 1 skipped
• final local browser E2E was not run because ASP.NET/Vite were unavailable in the final review session
• LOC checker passed with accepted warnings
• rg "window\.confirm" no matches
• rg "\bconfirm\(" reviewed shared confirm usages only
• browser-direct provider scan found no Trip Editor frontend direct external provider calls
• git diff --check origin/main...HEAD passed

Note

• noreply@wayfarer.app remains only in pre-existing tile-provider code/tests, not in geocode code/options/tests.
• The one E2E skip is the existing fixture-dependent sidebar shadow-child check.

[stef-k]

Final pre-merge review after ec7d59e:

• No blocking findings remain after the in-flight Search fix in ec7d59e.
• GitHub checks passed.
• Full/focused browser E2E passed earlier in the branch; final local browser E2E rerun was unavailable because ASP.NET/Vite were not available in the final review session.
• Scope remained geocode proxy/search-add only.
• Confirmed no browser-direct Nominatim/external provider calls and no fake provider contact identity in the geocode implementation.