feat: integrate KordantSpamShieldExtension target and complete App Review compliance (Task 28)

- Add KordantSpamShieldExtension target to project.yml with proper
  app-extension type, bundle identifier, and deployment target
- Create CallKit + App Group entitlements for SpamShield extension
- Move SpamDirectoryService to Sources/Shared for cross-target access
- Update app-review-checklist with 5 new technical items (total: 121)
- Update rejection-risk-mitigation with extension build integration
- Add SpamShield extension details to reviewer notes
- Mark Task 24 (push deep links) and Task 28 as complete

tasks/ios-production/README.md

@@ -40,7 +40,7 @@ Status legend: [ ] todo, [~] in-progress, [x] done
 - [x] 21 — Real API Client Wiring (Replace StubAPIClient) → `21-real-api-client.md`
 - [~] 22 — Token Refresh & Session Management → `22-token-refresh.md`
 - [~] 23 — Offline Mode & Sync Conflict Resolution → `23-offline-sync.md`
-- [~] 24 — Push Notification Deep Linking → `24-push-deep-links.md`
+- [x] 24 — Push Notification Deep Linking → `24-push-deep-links.md`
 
 ### App Store Compliance
 - [x] 25 — Privacy Manifest & Nutrition Labels → `25-privacy-manifest.md`