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/types/index.ts

@@ -98,7 +98,95 @@ export interface ExplainResult {
   "Execution Time": number;
 }
 
-export type TabType = "query" | "table" | "structure";
+export interface DatabaseInfo {
+  name: string;
+  owner: string;
+  encoding: string;
+  collation: string;
+  ctype: string;
+  tablespace: string;
+  connection_limit: number;
+  size: string;
+  description: string | null;
+}
+
+export interface CreateDatabaseParams {
+  name: string;
+  owner?: string;
+  template?: string;
+  encoding?: string;
+  tablespace?: string;
+  connection_limit?: number;
+}
+
+export interface RoleInfo {
+  name: string;
+  is_superuser: boolean;
+  can_login: boolean;
+  can_create_db: boolean;
+  can_create_role: boolean;
+  inherit: boolean;
+  is_replication: boolean;
+  connection_limit: number;
+  password_set: boolean;
+  valid_until: string | null;
+  member_of: string[];
+  members: string[];
+  description: string | null;
+}
+
+export interface CreateRoleParams {
+  name: string;
+  password?: string;
+  login: boolean;
+  superuser: boolean;
+  createdb: boolean;
+  createrole: boolean;
+  inherit: boolean;
+  replication: boolean;
+  connection_limit?: number;
+  valid_until?: string;
+  in_roles: string[];
+}
+
+export interface AlterRoleParams {
+  name: string;
+  password?: string;
+  login?: boolean;
+  superuser?: boolean;
+  createdb?: boolean;
+  createrole?: boolean;
+  inherit?: boolean;
+  replication?: boolean;
+  connection_limit?: number;
+  valid_until?: string;
+  rename_to?: string;
+}
+
+export interface TablePrivilege {
+  grantee: string;
+  table_schema: string;
+  table_name: string;
+  privilege_type: string;
+  is_grantable: boolean;
+}
+
+export interface GrantRevokeParams {
+  action: string;
+  privileges: string[];
+  object_type: string;
+  object_name: string;
+  role_name: string;
+  with_grant_option: boolean;
+}
+
+export interface RoleMembershipParams {
+  action: string;
+  role_name: string;
+  member_name: string;
+}
+
+export type TabType = "query" | "table" | "structure" | "roles";
 
 export interface Tab {
   id: string;
@@ -108,4 +196,5 @@ export interface Tab {
   schema?: string;
   table?: string;
   sql?: string;
+  roleName?: string;
 }