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>

internal/grpcserver/grpcserver.go

@@ -118,6 +118,7 @@ func (s *Server) buildServer(extra ...grpc.ServerOption) *grpc.Server {
 	mciasv1.RegisterAccountServiceServer(srv, &accountServiceServer{s: s})
 	mciasv1.RegisterCredentialServiceServer(srv, &credentialServiceServer{s: s})
 	mciasv1.RegisterPolicyServiceServer(srv, &policyServiceServer{s: s})
+	mciasv1.RegisterSSOClientServiceServer(srv, &ssoClientServiceServer{s: s})
 
 	return srv
 }