migrate dashboard to real HeroUI v3 components and neutral theme

The frontend was built against HeroUI v2 props/classes (variant="light"/"flat",
color="primary", startContent, text-tiny, <Avatar src=/name=>) while
@heroui/react ^3.2.1 is installed, so most styling was silently ignored.
Rewrites every page/component onto the actual v3 API (variant/color enums,
Tooltip/Dropdown trigger-content structure, Avatar.Image/Fallback via a new
AppAvatar helper) and replaces the custom orange branding with HeroUI's
neutral default theme tokens. Also compacts the dashboard stat tiles, narrows
the sidebar, and swaps the activity stat grid for a single-hue comparison bar
chart.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/pages/Settings.tsx

@@ -9,7 +9,7 @@ export function SettingsPage() {
   return (
     <SectionCard title="Einstellungen & Logging" subtitle="Globale Guild-Settings und Log-Kategorien">
       <div className="grid gap-5 xl:grid-cols-2">
-        <Card className="border border-default-100 bg-default-50/20">
+        <Card>
           <CardHeader className="px-5 pt-5 pb-0">
             <h3 className="text-base font-semibold">Allgemein</h3>
           </CardHeader>
@@ -43,13 +43,13 @@ export function SettingsPage() {
 
             <Separator />
 
-            <Button color="primary" startContent={<Save size={16} />} onPress={() => saveSettingsPayload(settings, 'Settings gespeichert')}>
-              Speichern
+            <Button variant="primary" onPress={() => saveSettingsPayload(settings, 'Settings gespeichert')}>
+              <Save size={16} /> Speichern
             </Button>
           </CardContent>
         </Card>
 
-        <Card className="border border-default-100 bg-default-50/20">
+        <Card>
           <CardHeader className="px-5 pt-5 pb-0">
             <h3 className="text-base font-semibold">Logging Kategorien</h3>
           </CardHeader>
@@ -76,8 +76,8 @@ export function SettingsPage() {
 
             <Separator />
 
-            <Button color="primary" startContent={<Save size={16} />} onPress={() => saveSettingsPayload(settings, 'Settings gespeichert')}>
-              Speichern
+            <Button variant="primary" onPress={() => saveSettingsPayload(settings, 'Settings gespeichert')}>
+              <Save size={16} /> Speichern
             </Button>
           </CardContent>
         </Card>