semi implemented and features implemented save checkpoint

docs/features/unchecked/platform/platform-service-aggregation-layer.md

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+# Platform Service Aggregation Layer
+
+## Module
+Platform
+
+## Status
+IMPLEMENTED
+
+## Description
+Backend Platform Service acting as aggregation layer for health status, quotas, onboarding progress, user preferences, and global search across all modules.
+
+## Implementation Details
+- **PlatformEndpoints**: `src/Platform/StellaOps.Platform.WebService/Endpoints/PlatformEndpoints.cs` -- REST API at `/api/v1/platform` with 6 endpoint groups: health (summary/dependencies/incidents/metrics), quotas (summary/tenants/alerts), onboarding (status/complete/skip), preferences (dashboard/profiles), search, metadata; all with tenant-scoped authorization policies
+- **PlatformHealthService**: `src/Platform/StellaOps.Platform.WebService/Services/PlatformHealthService.cs` -- aggregates health status from all platform services
+- **PlatformQuotaService**: service for quota tracking with alert management (create alert thresholds per tenant)
+- **PlatformOnboardingService**: `src/Platform/StellaOps.Platform.WebService/Services/PlatformOnboardingService.cs` -- tracks onboarding progress with step completion and skip support
+- **PlatformPreferencesService**: `src/Platform/StellaOps.Platform.WebService/Services/PlatformPreferencesService.cs` -- user dashboard preferences with profile management (CRUD)
+- **PlatformSearchService**: global search across all modules with source filtering, pagination
+- **PlatformMetadataService**: `src/Platform/StellaOps.Platform.WebService/Services/PlatformMetadataService.cs` -- platform metadata retrieval
+- **PlatformCache**: `src/Platform/StellaOps.Platform.WebService/Services/PlatformCache.cs` -- caching layer with TTL and data-as-of timestamps
+- **Source**: SPRINT_20251229_043_PLATFORM_platform_service_foundation
+
+## E2E Test Plan
+- [ ] Verify health summary endpoint aggregates all service statuses
+- [ ] Test quota alerts are created and returned with proper authorization
+- [ ] Verify onboarding step completion transitions correctly
+- [ ] Test global search returns results from multiple sources with pagination
+- [ ] Verify dashboard preferences persist and load per tenant/user