feat(broadcasts): add admin broadcast page and user opt-out switch

Admin page /admin/broadcasts to write, test and send broadcasts in both
languages; confirms the recipient count before send. History shows the
counts. A new switch in settings lets users opt out of platform mails;
account mails always come. Subject and body are plain text only.

src/components/AppHeader.jsx

@@ -1,7 +1,7 @@
 import {useEffect, useState} from 'react';
 import {Link, NavLink, useLocation, useNavigate} from 'react-router-dom';
 import {useTranslation} from 'react-i18next';
-import {ChartColumn, Coins, Dices, Eye, Languages, LayoutDashboard, Library, LogOut, Megaphone, Moon, Newspaper, Settings, Shield, Sun} from 'lucide-react';
+import {ChartColumn, Coins, Dices, Eye, Languages, LayoutDashboard, Library, LogOut, Mail, Megaphone, Moon, Newspaper, Settings, Shield, Sun} from 'lucide-react';
 import {toast} from 'sonner';
 
 import {Badge} from '@/components/ui/badge';
@@ -169,6 +169,9 @@ export default function AppHeader({isAuthenticated, onLogout}) {
                                         <DropdownMenuItem asChild>
                                             <Link to="/admin/news"><Newspaper/>{t('NAV.ADMIN_NEWS')}</Link>
                                         </DropdownMenuItem>
+                                        <DropdownMenuItem asChild>
+                                            <Link to="/admin/broadcasts"><Mail/>{t('NAV.ADMIN_BROADCASTS')}</Link>
+                                        </DropdownMenuItem>
                                     </>
                                 )}
                                 {isAdmin && (

src/components/AppHeader.test.jsx

@@ -55,6 +55,7 @@ describe('AppHeader', () => {
 
         expect(await screen.findByText('NAV.ADMIN')).toBeTruthy();
         expect(screen.getByText('NAV.ADMIN_NEWS')).toBeTruthy();
+        expect(screen.getByText('NAV.ADMIN_BROADCASTS')).toBeTruthy();
         expect(screen.getByText('NAV.VIEW_AS.MENU')).toBeTruthy();
         expect(screen.queryByText('NAV.VIEW_AS.BADGE')).toBeNull();
         expect(screen.queryByLabelText('NAV.PENDING_REQUESTS:0')).toBeNull();
@@ -84,6 +85,7 @@ describe('AppHeader', () => {
         openMenu();
         expect(await screen.findByText('NAV.VIEW_AS.MENU')).toBeTruthy();
         expect(screen.queryByText('NAV.ADMIN')).toBeNull();
+        expect(screen.queryByText('NAV.ADMIN_BROADCASTS')).toBeNull();
     });
 
     it('offers nothing of that to a user', async () => {
@@ -96,6 +98,7 @@ describe('AppHeader', () => {
         expect(screen.getByText('NAV.WHATS_NEW')).toBeTruthy();
         expect(screen.queryByText('NAV.ADMIN')).toBeNull();
         expect(screen.queryByText('NAV.ADMIN_NEWS')).toBeNull();
+        expect(screen.queryByText('NAV.ADMIN_BROADCASTS')).toBeNull();
         expect(screen.queryByText('NAV.VIEW_AS.MENU')).toBeNull();
     });
 });

src/components/PreferencesCard.jsx

@@ -11,7 +11,7 @@ import {usePreferences} from '../context/PreferencesContext.jsx';
 import usePersistSettings from '../hooks/usePersistSettings.js';
 import useSaveResponse from '../hooks/useSaveResponse.js';
 import {FAVORITE_PLATFORMS, saveFavoritePlatform} from '../utils/platforms.js';
-import {LANGUAGES, saveSettings} from '../utils/settings.js';
+import {LANGUAGES, savePlatformMails, saveSettings} from '../utils/settings.js';
 
 // Radix Select has no empty value.
 const NO_FAVORITE = 'NONE';
@@ -41,6 +41,13 @@ export default function PreferencesCard() {
         }
     };
 
+    const handlePlatformMailsChange = async (next) => {
+        if (await runSave(() => savePlatformMails(next))) {
+            updateProfile((p) => ({...p, settings: {...p.settings, platformMails: next}}));
+            toast.success(t('SETTINGS.SAVED'));
+        }
+    };
+
     return (
         <Card>
             <CardHeader>
@@ -83,6 +90,14 @@ export default function PreferencesCard() {
                         </SelectContent>
                     </Select>
                 </div>
+                <div className="flex items-center justify-between gap-4">
+                    <div className="space-y-1">
+                        <Label htmlFor="platformMails">{t('SETTINGS.PLATFORM_MAILS')}</Label>
+                        <p className="text-xs text-muted-foreground">{t('SETTINGS.PLATFORM_MAILS_HINT')}</p>
+                    </div>
+                    <Switch id="platformMails" checked={profile?.settings?.platformMails ?? true}
+                            onCheckedChange={handlePlatformMailsChange}/>
+                </div>
             </CardContent>
         </Card>
     );