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.

app/layout.tsx

@@ -3,10 +3,8 @@ import { unstable_noStore as noStore } from "next/cache";
 import localFont from "next/font/local";
 import Script from "next/script";
 import { getLocale } from "next-intl/server";
-import { QueryToastBridge } from "@/components/admin/query-toast-bridge";
 import { SoundProvider } from "@/components/sound-provider";
 import { ThemeProvider } from "@/components/theme-provider";
-import { Toaster } from "@/components/ui/toaster";
 import { getSiteSettings } from "@/lib/app-config";
 import { buildAppMetadata } from "@/lib/metadata";
 import { getDirection } from "@/lib/locale";
@@ -96,8 +94,6 @@ export default async function RootLayout({
         <ThemeProvider>
           <SoundProvider>
             {children}
-            <QueryToastBridge />
-            <Toaster locale={locale} />
           </SoundProvider>
         </ThemeProvider>
         <Script