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/site/contact-form.tsx

@@ -2,12 +2,10 @@
 
 import Link from "next/link";
 
-import { ContactTurnstile } from "@/components/site/contact-turnstile";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { Textarea } from "@/components/ui/textarea";
-import type { PublicContactProtectionSettings } from "@/lib/contact-protection";
 
 type ContactFormCopy = {
   name: string;
@@ -25,7 +23,6 @@ type ContactFormProps = {
   locale: string;
   previewHref: string;
   copy: ContactFormCopy;
-  protection: PublicContactProtectionSettings;
 };
 
 export function ContactForm({
@@ -33,7 +30,6 @@ export function ContactForm({
   locale,
   previewHref,
   copy,
-  protection,
 }: ContactFormProps) {
   return (
     <form action={action} className="grid gap-5">
@@ -68,10 +64,6 @@ export function ContactForm({
 
       <p className="text-sm text-muted-foreground">{copy.note}</p>
 
-      {protection.turnstile.enabled ? (
-        <ContactTurnstile siteKey={protection.turnstile.siteKey} />
-      ) : null}
-
       <div className="flex flex-wrap gap-3">
         <Button type="submit">{copy.submit}</Button>
         <Button asChild variant="outline">