feat: complete E2E deployment flow with storage layered config and values template versioning

- Instance deployment: charts browser, deploy modal, instances list
- Values Template version management (create/history/rollback)
- Storage layered config (cluster > workspace > shared priority)
- Cluster credential decryptIfNeeded for mixed encrypted/plaintext kubeconfig
- YAML syntax validation (client-side + server-side warning)
- Frontend: charts, instances, storage, templates, admin pages
- Backend: storage service, instance service, cluster service, helm client
- Multi-Tenant Kubeconfig.md: added by user

backend/scripts/migrations/20250418_add_cluster_storage.sql

@@ -0,0 +1,15 @@
+-- Migration: Add cluster_id to storage_backends for layered storage config
+-- This enables storage backends to be associated with specific clusters
+-- Priority order: User Override > Workspace Default > Cluster Default > Shared Storage
+
+-- Add cluster_id column to storage_backends table
+ALTER TABLE storage_backends ADD COLUMN IF NOT EXISTS cluster_id VARCHAR(36) REFERENCES clusters(id) ON DELETE SET NULL;
+
+-- Index for faster lookups by cluster
+CREATE INDEX IF NOT EXISTS idx_storage_backends_cluster ON storage_backends(cluster_id);
+
+-- Composite index for cluster + default storage lookup
+CREATE INDEX IF NOT EXISTS idx_storage_backends_default_cluster ON storage_backends(cluster_id, is_default) WHERE cluster_id IS NOT NULL;
+
+-- Add comment for documentation
+COMMENT ON COLUMN storage_backends.cluster_id IS 'Associated cluster ID for cluster-level default storage. NULL means workspace or shared storage.';