feat(flutter/admin): users + invites mutations

Extends AdminUsersController (build-only since slice 2) with setAdmin,
setAutoApprove, delete, resetPassword. is_admin/auto_approve toggles
optimistically swap the row and roll back on server error (including
the last-admin guard 4xx). resetPassword is admin-supplied; no
auto-generation mode exists server-side.

Adds AdminInvitesController + adminInvitesProvider with create
(prepends new invite to the list, returns it for the copy-once
dialog) and revoke (optimistic remove + rollback).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/admin/admin_providers.dart

@@ -8,6 +8,7 @@ import '../library/library_providers.dart' show dioProvider;
 import '../models/admin_quarantine_item.dart';
 import '../models/admin_request.dart';
 import '../models/admin_user.dart';
+import '../models/invite.dart';
 
 final adminRequestsApiProvider = FutureProvider<AdminRequestsApi>((ref) async {
   return AdminRequestsApi(await ref.watch(dioProvider.future));
@@ -92,16 +93,73 @@ final adminRequestsProvider =
     AsyncNotifierProvider<AdminRequestsController, List<AdminRequest>>(
         AdminRequestsController.new);
 
-/// Read side defined here so the Requests screen can join requester
-/// UUID → username for display. Mutation methods (setAdmin,
-/// setAutoApprove, resetPassword, delete) are appended in Slice 3
-/// alongside the Users screen.
+/// Read side originally defined for the Requests screen's
+/// requester-UUID → username join. Mutation methods (setAdmin,
+/// setAutoApprove, resetPassword, delete) added alongside the Users
+/// screen in Slice 3. resetPassword is admin-supplies; the server
+/// has no auto-generation mode.
 class AdminUsersController extends AsyncNotifier<List<AdminUser>> {
   @override
   Future<List<AdminUser>> build() async {
     final api = await ref.watch(adminUsersApiProvider.future);
     return api.list();
   }
+
+  /// Optimistic flip of `is_admin` on the user row; rolls back on
+  /// server error (including the last-admin guard 4xx).
+  Future<void> setAdmin(String id, bool isAdmin) =>
+      _patch(id, (u) => _copy(u, isAdmin: isAdmin),
+          (api) => api.setAdmin(id, isAdmin));
+
+  Future<void> setAutoApprove(String id, bool autoApprove) =>
+      _patch(id, (u) => _copy(u, autoApproveRequests: autoApprove),
+          (api) => api.setAutoApprove(id, autoApprove));
+
+  Future<void> delete(String id) async {
+    final api = await ref.read(adminUsersApiProvider.future);
+    final current = state.value ?? const <AdminUser>[];
+    state = AsyncData(current.where((u) => u.id != id).toList());
+    try {
+      await api.delete(id);
+      ref.invalidate(adminCountsProvider);
+    } catch (e, st) {
+      state = AsyncData(current);
+      Error.throwWithStackTrace(e, st);
+    }
+  }
+
+  Future<void> resetPassword(String id, String newPassword) async {
+    final api = await ref.read(adminUsersApiProvider.future);
+    await api.resetPassword(id, newPassword);
+  }
+
+  Future<void> _patch(
+    String id,
+    AdminUser Function(AdminUser) mutate,
+    Future<void> Function(AdminUsersApi api) action,
+  ) async {
+    final api = await ref.read(adminUsersApiProvider.future);
+    final current = state.value ?? const <AdminUser>[];
+    state = AsyncData([
+      for (final u in current) u.id == id ? mutate(u) : u,
+    ]);
+    try {
+      await action(api);
+    } catch (e, st) {
+      state = AsyncData(current);
+      Error.throwWithStackTrace(e, st);
+    }
+  }
+
+  AdminUser _copy(AdminUser u, {bool? isAdmin, bool? autoApproveRequests}) =>
+      AdminUser(
+        id: u.id,
+        username: u.username,
+        displayName: u.displayName,
+        isAdmin: isAdmin ?? u.isAdmin,
+        autoApproveRequests: autoApproveRequests ?? u.autoApproveRequests,
+        createdAt: u.createdAt,
+      );
 }
 
 final adminUsersProvider =
@@ -142,3 +200,38 @@ class AdminQuarantineController
 
 final adminQuarantineProvider = AsyncNotifierProvider<AdminQuarantineController,
     List<AdminQuarantineItem>>(AdminQuarantineController.new);
+
+class AdminInvitesController extends AsyncNotifier<List<Invite>> {
+  @override
+  Future<List<Invite>> build() async {
+    final api = await ref.watch(adminInvitesApiProvider.future);
+    return api.list();
+  }
+
+  /// Returns the freshly-minted invite so the screen can show the
+  /// token in a copy-once dialog. The new invite is also prepended
+  /// to the local list so it shows up without a refresh.
+  Future<Invite> create({String? note}) async {
+    final api = await ref.read(adminInvitesApiProvider.future);
+    final invite = await api.create(note: note);
+    final current = state.value ?? const <Invite>[];
+    state = AsyncData([invite, ...current]);
+    return invite;
+  }
+
+  Future<void> revoke(String token) async {
+    final api = await ref.read(adminInvitesApiProvider.future);
+    final current = state.value ?? const <Invite>[];
+    state = AsyncData(current.where((i) => i.token != token).toList());
+    try {
+      await api.revoke(token);
+    } catch (e, st) {
+      state = AsyncData(current);
+      Error.throwWithStackTrace(e, st);
+    }
+  }
+}
+
+final adminInvitesProvider =
+    AsyncNotifierProvider<AdminInvitesController, List<Invite>>(
+        AdminInvitesController.new);