feat: consolidate database management work

Add catalog-owned logical relationships and runtime snapshots, extend the database-management UI and validation coverage, and document the updated operational workflow.

Keep active sensitive-generation status in a tooltip and indicator, and update the layout E2E to follow the history action in its new database-scoped location.

frontend/src/api/client.ts

@@ -35,6 +35,9 @@ const safeErrorCodes = new Set([
   "sensitive_data_suggestion_run_not_found",
   "schema_sync_conflict", "schema_introspection_failed", "schema_request_invalid",
   "schema_operation_failed", "sync_run_not_found", "table_stale", "column_stale",
+  "relationship_not_found", "relationship_duplicate", "relationship_target_not_unique",
+  "relationship_type_incompatible", "relationship_read_only", "relationship_request_invalid",
+  "relationship_operation_failed", "relationship_schema_stale", "column_not_found",
 ]);
 
 type SafeErrorPayload = {
@@ -104,6 +107,15 @@ const localCodeMessages: Record<string, string> = {
   sync_run_not_found: "The synchronization run was not found.",
   table_stale: "Table metadata changed. Reload and try again.",
   column_stale: "Column metadata changed. Reload and try again.",
+  relationship_not_found: "The relationship no longer exists. Refresh and try again.",
+  relationship_duplicate: "This relationship already exists.",
+  relationship_target_not_unique: "The target column must be the only primary-key column of its table.",
+  relationship_type_incompatible: "Source and target column types are not compatible.",
+  relationship_read_only: "Physical relationships are read-only.",
+  relationship_request_invalid: "The relationship request is invalid.",
+  relationship_operation_failed: "The relationship operation failed.",
+  relationship_schema_stale: "Synchronize the current database schema before managing logical relationships.",
+  column_not_found: "The selected catalog column was not found. Refresh and try again.",
 };
 
 const localStatusMessages: Record<number, string> = {