fix(contacts): queue VCF import saves

[keilogic]

Summary

Closes #834.

• Queue large VCF contact imports through a bounded save worker pool instead of starting every saveContact() request at once.
• Keep the existing one post-import reload() behavior from the earlier import-sync fix.
• Add focused regression coverage that verifies the import queue preserves all contacts while limiting concurrent saves.

Validation

• npm ci
• Red baseline before the implementation: npx ng test runbox7 --watch=false --browsers=FirefoxHeadless --include=src/app/contacts-app/contacts-app.component.spec.ts failed because runContactImportQueue did not exist.
• npx ng test runbox7 --watch=false --browsers=FirefoxHeadless --include=src/app/contacts-app/contacts-app.component.spec.ts passed with 2 SUCCESS.
• npx tsc -p src/tsconfig.app.json --noEmit
• npx tsc -p src/tsconfig.spec.json --noEmit
• npm run lint -- --quiet
• npm run policy passed for the current commits; it still reports existing historical commit-message warnings.
• git diff --check origin/master...HEAD
• git show --check --stat --oneline HEAD
• npx ng test runbox7 --watch=false --browsers=FirefoxHeadless passed with 247 SUCCESS and 2 existing skipped tests.
• SKIP_CHANGELOG=1; node src/build/pre-build.js; npx ng build --configuration production --base-href=/app/ runbox7; node src/build/post-build.js passed with existing Angular/CommonJS/theming warnings; build hash 50db6d881a05ba77.

AI Disclosure

I used OpenAI Codex to inspect the issue and current source, make the code/test changes, and run the validation commands listed above.