feat(nav): simplify navigation and terms (#57)

One glossary (docs/GLOSSARY.md) for all de and en texts.
Five nav items; phones get a bottom bar with labels.
Community page with following, followers, player search and stats.
The bell is the one place for notes, news and open questions.
Settings in tabs; auto-save is silent and rolls back on error.
Questions page explains itself; removed games are a library filter.
Own profile: menu link, public chip, copy link, private hint.
Points page starts with a short summary; stats use status colors.

src/components/PreferencesCard.jsx

@@ -1,17 +1,15 @@
 import {useTranslation} from 'react-i18next';
 import {SlidersHorizontal} from 'lucide-react';
-import {toast} from 'sonner';
 
 import {Card, CardContent, CardHeader, CardTitle} from '@/components/ui/card';
 import {Label} from '@/components/ui/label';
 import {Select, SelectContent, SelectItem, SelectTrigger, SelectValue} from '@/components/ui/select';
-import {Switch} from '@/components/ui/switch';
 import {useCurrentUserContext} from '../context/CurrentUserContext.jsx';
 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} from '../utils/settings.js';
 
 // Radix Select has no empty value.
 const NO_FAVORITE = 'NONE';
@@ -19,26 +17,22 @@ const NO_FAVORITE = 'NONE';
 export default function PreferencesCard() {
     const {t, i18n} = useTranslation();
     const {user: profile, updateUser: updateProfile} = useCurrentUserContext();
-    const {isDarkMode, setDarkMode, setLanguage} = usePreferences();
+    const {setLanguage} = usePreferences();
     const persistSettings = usePersistSettings();
     const runSave = useSaveResponse();
 
-    const handleDarkThemeToggle = async () => {
-        const next = !isDarkMode;
-        setDarkMode(next); // apply on the fly
-        await persistSettings(() => saveSettings({useDarkTheme: next}));
-    };
-
     const handleLanguageChange = async (next) => {
-        await persistSettings(() => setLanguage(next));
+        const previous = i18n.language;
+        const {ok} = await persistSettings(() => setLanguage(next), {silent: true});
+        if (!ok) i18n.changeLanguage(previous);
     };
 
     const handleFavoritePlatformChange = async (value) => {
         const platform = value === NO_FAVORITE ? null : value;
-        if (await runSave(() => saveFavoritePlatform(platform))) {
-            updateProfile((p) => ({...p, settings: {...p.settings, favoritePlatform: platform}}));
-            toast.success(t('SETTINGS.SAVED'));
-        }
+        const previous = profile?.settings?.favoritePlatform ?? null;
+        const setPlatform = (next) => updateProfile((p) => ({...p, settings: {...p.settings, favoritePlatform: next}}));
+        setPlatform(platform);
+        if (!await runSave(() => saveFavoritePlatform(platform))) setPlatform(previous);
     };
 
     return (
@@ -47,10 +41,6 @@ export default function PreferencesCard() {
                 <CardTitle className="flex items-center gap-2"><SlidersHorizontal className="size-4 text-primary"/>{t('SETTINGS.PREFERENCES')}</CardTitle>
             </CardHeader>
             <CardContent className="space-y-6">
-                <div className="flex items-center justify-between gap-4">
-                    <Label htmlFor="useDarkTheme">{t('SETTINGS.DARK_THEME')}</Label>
-                    <Switch id="useDarkTheme" checked={isDarkMode} onCheckedChange={handleDarkThemeToggle}/>
-                </div>
                 <div className="flex items-center justify-between gap-4">
                     <Label htmlFor="language">{t('SETTINGS.LANGUAGE')}</Label>
                     <Select value={i18n.language} onValueChange={handleLanguageChange}>