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.

components/layout/floating-preferences.tsx

@@ -27,15 +27,11 @@ export function FloatingPreferences({
           <SoundToggle
             ariaLabel={t("soundMute")}
             mutedAriaLabel={t("soundUnmute")}
-            mutedToastLabel={t("soundMuted")}
-            unmutedToastLabel={t("soundEnabled")}
             variant="ghost"
             className="h-9 w-9 rounded-pill border border-transparent bg-transparent text-foreground/80 hover:bg-accent hover:text-foreground"
           />
           <ThemeToggle
             ariaLabel={t("themeToggle")}
-            lightToastLabel={t("themeLight")}
-            darkToastLabel={t("themeDark")}
             variant="ghost"
             className="h-9 w-9 rounded-pill border border-transparent bg-transparent text-foreground/80 hover:bg-accent hover:text-foreground"
           />