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/BottomNav.jsx

@@ -0,0 +1,29 @@
+import {Link, useLocation} from 'react-router-dom';
+import {useTranslation} from 'react-i18next';
+
+import {cn} from '@/lib/utils';
+import {isNavActive, NAV_ITEMS} from './navItems.js';
+
+/**
+ * The main navigation on a phone: a bar at the bottom edge, every item with its label.
+ */
+export default function BottomNav() {
+    const {t} = useTranslation();
+    const {pathname} = useLocation();
+    return (
+        <nav aria-label={t('NAV.MENU')}
+             className="fixed inset-x-0 bottom-0 z-50 flex border-t bg-background/95 pb-[env(safe-area-inset-bottom)] backdrop-blur md:hidden">
+            {NAV_ITEMS.map((item) => {
+                const active = isNavActive(item, pathname);
+                return (
+                    <Link key={item.to} to={item.to} aria-current={active ? 'page' : undefined}
+                          className={cn('flex flex-1 flex-col items-center gap-0.5 py-2 text-[11px] font-medium',
+                              active ? 'text-primary' : 'text-muted-foreground')}>
+                        <item.Icon className="size-5"/>
+                        <span className="max-w-full truncate px-1">{t(item.labelKey)}</span>
+                    </Link>
+                );
+            })}
+        </nav>
+    );
+}