feat: add database, role & privilege management

Add Admin sidebar tab with database/role management panels, role manager
workspace tab, and privilege dialogs. Backend provides 10 new Tauri
commands for CRUD on databases, roles, and privileges with read-only
mode enforcement. Context menus on schema tree nodes allow dropping
databases and viewing/granting table privileges.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -2,6 +2,7 @@ mod commands;
 mod error;
 mod models;
 mod state;
+mod utils;
 
 use state::AppState;
 
@@ -43,6 +44,17 @@ pub fn run() {
             // export
             commands::export::export_csv,
             commands::export::export_json,
+            // management
+            commands::management::get_database_info,
+            commands::management::create_database,
+            commands::management::drop_database,
+            commands::management::list_roles,
+            commands::management::create_role,
+            commands::management::alter_role,
+            commands::management::drop_role,
+            commands::management::get_table_privileges,
+            commands::management::grant_revoke,
+            commands::management::manage_role_membership,
             // history
             commands::history::add_history_entry,
             commands::history::get_history,