feat: add proper Pydantic response_model to all stats endpoints

- Create comprehensive stats schemas in models/schema/stats.py:
  - ImportStatsResponse, UserStatsResponse, ProductStatsResponse
  - PlatformStatsResponse, AdminDashboardResponse
  - VendorDashboardStatsResponse with nested models
  - VendorAnalyticsResponse, CodeQualityDashboardStatsResponse
- Move DashboardStatsResponse from code_quality.py to schema file
- Fix get_vendor_statistics() to return pending_vendors field
- Fix get_vendor_stats() to return flat structure matching schema
- Add response_model to all stats endpoints:
  - GET /admin/dashboard -> AdminDashboardResponse
  - GET /admin/dashboard/stats/platform -> PlatformStatsResponse
  - GET /admin/marketplace-import-jobs/stats -> ImportStatsResponse
  - GET /vendor/dashboard/stats -> VendorDashboardStatsResponse
  - GET /vendor/analytics -> VendorAnalyticsResponse
- Enhance API-001 architecture rule with detailed guidance
- Add SVC-007 rule for service/schema compatibility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/v1/admin/vendors.py

@@ -109,11 +109,12 @@ def get_vendor_statistics_endpoint(
     """Get vendor statistics for admin dashboard (Admin only)."""
     stats = stats_service.get_vendor_statistics(db)
 
+    # Use schema-compatible keys (with fallback to legacy keys)
     return VendorStatsResponse(
-        total=stats.get("total_vendors", 0),
-        verified=stats.get("verified_vendors", 0),
-        pending=stats.get("pending_vendors", 0),
-        inactive=stats.get("inactive_vendors", 0),
+        total=stats.get("total", stats.get("total_vendors", 0)),
+        verified=stats.get("verified", stats.get("verified_vendors", 0)),
+        pending=stats.get("pending", stats.get("pending_vendors", 0)),
+        inactive=stats.get("inactive", stats.get("inactive_vendors", 0)),
     )