Move SSO clients from config to database

- Add sso_clients table (migration 000010) with client_id, redirect_uri,
  tags (JSON), enabled flag, and audit timestamps
- Add SSOClient model struct and audit events
- Implement DB CRUD with 10 unit tests
- Add REST API: GET/POST/PATCH/DELETE /v1/sso/clients (policy-gated)
- Add gRPC SSOClientService with 5 RPCs (admin-only)
- Add mciasctl sso list/create/get/update/delete commands
- Add web UI admin page at /sso-clients with HTMX create/toggle/delete
- Migrate handleSSOAuthorize and handleSSOTokenExchange to use DB
- Remove SSOConfig, SSOClient struct, lookup methods from config
- Simplify: client_id = service_name for policy evaluation

Security:
- SSO client CRUD is admin-only (policy-gated REST, requireAdmin gRPC)
- redirect_uri must use https:// (validated at DB layer)
- Disabled clients are rejected at both authorize and token exchange
- All mutations write audit events

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

proto/generate.go

@@ -6,5 +6,5 @@
 //
 // Prerequisites: protoc, protoc-gen-go, protoc-gen-go-grpc must be in PATH.
 //
-//go:generate protoc --proto_path=../proto --go_out=../gen --go_opt=paths=source_relative --go-grpc_out=../gen --go-grpc_opt=paths=source_relative mcias/v1/common.proto mcias/v1/admin.proto mcias/v1/auth.proto mcias/v1/token.proto mcias/v1/account.proto mcias/v1/policy.proto
+//go:generate protoc --proto_path=../proto --go_out=../gen --go_opt=paths=source_relative --go-grpc_out=../gen --go-grpc_opt=paths=source_relative mcias/v1/common.proto mcias/v1/admin.proto mcias/v1/auth.proto mcias/v1/token.proto mcias/v1/account.proto mcias/v1/policy.proto mcias/v1/sso_client.proto
 package proto