feat(build): add /build skill — universal TDD-first feature implementation command

Adds a Cursor slash command that implements any feature end-to-end:
deep research → TDD (Red/Green/Refactor) → integration test generation
with device pause gate → external setup checklist → verified PR.

Includes a FEATURE_REGISTRY covering 7 feature types (notifications,
auth, payments, deep links, analytics, storage, camera/media) with
per-type test scenarios, external setup steps, and files-to-touch.
Stack-aware: adapts to architecture, state management, backend,
platforms, and e2e tool from project-brief.yaml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

flutter-cursor-templates/generator/src/resolver.dart

@@ -72,6 +72,7 @@ class Resolver {
       'skills/scaffold-feature',
       'skills/scaffold-screen',
       'skills/generate-tests',
+      'skills/build',
     ]);
     if (brief.apiDocsFormat != 'none') files.add('skills/generate-api-client');
     if (brief.flavors.length > 1)      files.add('skills/create-flavor');
@@ -123,6 +124,7 @@ class Resolver {
     if (key.contains('i18n'))           return 'localization.enabled: true';
     if (key.contains('migration'))      return 'state_management is GetX — migration guidance included';
     if (key.contains('security-agent')) return 'scale: ${brief.scale} or auth is configured';
+    if (key == 'skills/build')           return 'Always included — universal TDD-first feature implementation command';
     if (key.contains('api-client'))     return 'api_docs.format is set';
     if (key.contains('realtime'))       return 'features.special contains realtime';
     return 'Included';