refactor: drop toast + over-engineered extras, add inline admin feedback

Phase 1 cleanup of the personal-site revamp. Backend/architecture untouched;
changes are limited to removing unused complexity and restoring feedback.

Removals
- Toast system: delete react-hot-toast, Toaster, QueryToastBridge, lib/toast,
  the toggle/easter-egg calls, related i18n keys and the dependency.
- Contact protection: remove Turnstile + per-IP rate limiting
  (lib/contact-guard, lib/contact-protection, admin screen, form widget,
  app-config wiring, nav entry, test).
- Speculative specs: delete orders, products, downloads, project-inquiry.

Inline feedback (replaces toast, no new deps)
- Add lib/admin-feedback (withFlash/readFlash) and components/admin/admin-flash,
  rendered centrally by AdminDashboardShell.
- Emit success/error messages for media, site-settings, portfolio, smtp,
  marquee and maintenance actions; pages read them via searchParams.
- Contact form shows validation/delivery errors inline; success still
  redirects to /success.

Docs
- Fix stale paths in frontend-system-* (components/root -> components/admin,
  lib/root-navigation -> lib/admin-navigation, drop phantom src/) and remove
  contact-protection references from docs and CLAUDE.md.
- Add docs/PHASE0_DIAGNOSIS.md (diagnosis report).

Note: proxy.ts self-fetch kept intentionally; it also drives maintenance mode.

messages/de.json

@@ -10,16 +10,8 @@
     "openMenu": "Menü öffnen",
     "closeMenu": "Menü schliessen",
     "themeToggle": "Theme wechseln",
-    "themeLight": "Heller Modus aktiviert",
-    "themeDark": "Dunkler Modus aktiviert",
     "soundMute": "Sounds stummschalten",
-    "soundUnmute": "Sounds aktivieren",
-    "soundMuted": "Sound stummgeschaltet",
-    "soundEnabled": "Sound aktiviert",
-    "localeChangedDe": "Sprache auf Deutsch gewechselt",
-    "localeChangedEn": "Sprache auf Englisch gewechselt",
-    "localeChangedAr": "Sprache auf Arabisch gewechselt",
-    "logoTripleClick": "Ganz ruhig. Das Logo ist kein Panikknopf."
+    "soundUnmute": "Sounds aktivieren"
   },
   "footer": {
     "line": {