feat(04-01): redesign LoginPage with brand presence and OAuth icons

- Change background from bg-background to bg-muted/60
- Add border-t-4 border-t-primary shadow-lg card accent
- Add favicon.svg logo above CardTitle
- Add auth.loginSubtitle below title
- Add Google SVG icon and GitHub SVG icon to OAuth buttons
- Add gap-2 to OAuth button className for icon/text spacing
- Add auth.loginSubtitle and auth.registerSubtitle to en.json and de.json

src/i18n/de.json

@@ -19,7 +19,9 @@
     "displayName": "Anzeigename",
     "noAccount": "Noch kein Konto?",
     "hasAccount": "Bereits ein Konto?",
-    "orContinueWith": "Oder weiter mit"
+    "orContinueWith": "Oder weiter mit",
+    "loginSubtitle": "Melde dich bei deinem Konto an",
+    "registerSubtitle": "Erstelle ein neues Konto"
   },
   "categories": {
     "title": "Kategorien",

src/i18n/en.json

@@ -19,7 +19,9 @@
     "displayName": "Display Name",
     "noAccount": "Don't have an account?",
     "hasAccount": "Already have an account?",
-    "orContinueWith": "Or continue with"
+    "orContinueWith": "Or continue with",
+    "loginSubtitle": "Sign in to your account",
+    "registerSubtitle": "Create a new account"
   },
   "categories": {
     "title": "Categories",