feat(api): Implement API Resource Standard compliance

- Create BaseResource with formatDate() and formatDecimal() utilities
- Create 11 API Resource classes for all models
- Update all 6 controllers to return wrapped responses via wrapResource()
- Update frontend API client with unwrapResponse() helper
- Update all 63+ backend tests to expect 'data' wrapper
- Regenerate Scribe API documentation

BREAKING CHANGE: All API responses now wrap data in 'data' key per architecture spec.

Backend Tests: 70 passed, 5 failed (unrelated to data wrapper)
Frontend Unit: 10 passed
E2E Tests: 102 passed, 20 skipped
API Docs: Generated successfully

Refs: openspec/changes/api-resource-standard

openspec/changes/api-resource-standard/proposal.md

@@ -0,0 +1,58 @@
+## Why
+
+The Headroom API currently returns raw JSON responses without a standardized wrapper. This violates the architecture specification (docs/headroom-architecture.md, lines 315-393) which mandates Laravel API Resources for consistent JSON structure. This technical debt creates several problems:
+
+1. **Inconsistent Response Format**: Some endpoints return arrays, others objects, making client-side parsing error-prone
+2. **No Future-Proofing**: Adding metadata (pagination, relationships, meta) requires breaking changes later
+3. **Missing Data Wrapper**: Architecture requires `"data"` key for all responses to support future transformations
+4. **No Resource Abstraction**: Direct model exposure limits ability to transform data without breaking clients
+
+Since the application is pre-production and not in active use, we should fix this now to avoid permanent technical debt.
+
+## What Changes
+
+### Breaking Changes
+- **BREAKING**: All API responses will be wrapped in `"data"` key
+- **BREAKING**: Collections will use Laravel's resource collection format with `"data"` array
+- **BREAKING**: Frontend API client must unwrap `response.data` instead of direct access
+
+### New Components
+- Create `app/Http/Resources/` directory structure
+- Create 11 API Resource classes for consistent transformation
+- Create base `BaseResource` with common formatting utilities
+
+### Updated Components
+- Update 6 controllers to use API Resources instead of `response()->json()`
+- Update 63 backend tests to expect `"data"` wrapper in responses
+- Update frontend API client to handle new response format
+- Regenerate Scribe API documentation
+
+## Capabilities
+
+### New Capabilities
+- `api-resource-standard`: Standardize all API responses using Laravel API Resources with consistent `"data"` wrapper
+
+### Modified Capabilities
+- *(none - this is a refactoring change, no functional requirements change)*
+
+## Impact
+
+### Backend (Laravel)
+- **Files Created**: 11 new resource classes in `app/Http/Resources/`
+- **Files Modified**: 6 controllers in `app/Http/Controllers/Api/`
+- **Tests Updated**: 63 feature tests
+- **New Tests**: 11+ unit tests for resource classes
+
+### Frontend (SvelteKit)
+- **Files Modified**: API client in `src/lib/api/` directory
+- **Breaking**: All API calls must access `response.json().data` instead of `response.json()`
+
+### Documentation
+- **Regenerated**: Scribe API docs will show new response format
+
+### Dependencies
+- No new dependencies required (Laravel's built-in API Resources)
+
+### Performance
+- Minimal impact - API Resources add negligible overhead
+- Slight improvement: Consistent caching keys can be optimized