fix(clickhouse): validate auth in test_connection and disable transactions

- test_connection now uses SELECT 1 instead of /ping which doesn't
  require authentication, so wrong passwords are caught early
- Disable transaction support for ClickHouse (no BEGIN/COMMIT)
- Mark ClickHouse tables as non-insertable (no row-level operations)

src/lib/databaseTableDataCapabilities.ts

@@ -66,6 +66,15 @@ const DATABASE_CAPABILITY_OVERRIDES: Partial<Record<DatabaseType, Partial<Databa
       transaction: false,
     },
   },
+  clickhouse: {
+    tableData: {
+      insert: false,
+      updateRequiresPrimaryKey: true,
+      deleteRequiresPrimaryKey: true,
+      requiresTransactionalTableForExistingRows: false,
+      transaction: false,
+    },
+  },
 };
 
 export function getDatabaseCapability(dbType?: DatabaseType): DatabaseCapability {