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/admin/admin-dashboard-shell.tsx

@@ -15,6 +15,7 @@ import {
 } from "lucide-react";
 import Link from "next/link";
 
+import { AdminFlash } from "@/components/admin/admin-flash";
 import { DashboardLayout } from "@/components/dashboard/dashboard-layout";
 import { MotionFade } from "@/components/motion-fade";
 import { SidebarMaintenanceControl } from "@/components/admin/sidebar-maintenance-control";
@@ -24,6 +25,7 @@ import { Button } from "@/components/ui/button";
 import { buildSiteUrl, getAdminAppPath } from "@/lib/admin-routing";
 import { getMaintenanceMode, getSiteSettingsMediaBindings } from "@/lib/app-config";
 import { getAdminNavigation } from "@/lib/admin-navigation";
+import type { FlashMessages } from "@/lib/admin-feedback";
 
 import { updateMaintenanceModeAction } from "@/app/_admin/maintenance/actions";
 
@@ -40,7 +42,6 @@ type AdminDashboardCopy = {
   localizationSettings?: string;
   marquee?: string;
   smtp?: string;
-  contactProtection?: string;
   logout: string;
   backToSite: string;
 };
@@ -48,9 +49,9 @@ type AdminDashboardCopy = {
 type AdminDashboardShellProps = {
   copy: AdminDashboardCopy;
   active: "overview" | "maintenance" | "ui-kit" | "portfolio" | "media" | "site-settings" | "smtp" | "marquee";
-  smtpChild?: "settings" | "contact-protection";
   portfolioChild?: "overview" | "projects" | "new-project" | "categories";
   siteSettingsChild?: "brand" | "localization";
+  flash?: FlashMessages;
   logoutAction: () => Promise<void>;
   headerTitle: string;
   headerDescription: string;
@@ -63,9 +64,9 @@ type AdminDashboardShellProps = {
 export async function AdminDashboardShell({
   copy,
   active,
-  smtpChild,
   portfolioChild,
   siteSettingsChild,
+  flash,
   logoutAction,
   headerTitle,
   headerDescription,
@@ -78,7 +79,7 @@ export async function AdminDashboardShell({
     getSiteSettingsMediaBindings(),
     getMaintenanceMode(),
   ]);
-  const sidebarItems = getAdminNavigation(copy, active, smtpChild, portfolioChild, siteSettingsChild);
+  const sidebarItems = getAdminNavigation(copy, active, portfolioChild, siteSettingsChild);
   const normalizedSidebarItems = sidebarItems.filter(
     (item) =>
       item.href !== getAdminAppPath("/maintenance") &&
@@ -155,18 +156,19 @@ export async function AdminDashboardShell({
           <SoundToggle
             ariaLabel="Mute sounds"
             mutedAriaLabel="Unmute sounds"
-            mutedToastLabel="Sound muted"
-            unmutedToastLabel="Sound enabled"
           />
           <ThemeToggle
             ariaLabel="Theme wechseln"
-            lightToastLabel="Light mode enabled"
-            darkToastLabel="Dark mode enabled"
           />
         </div>
       }
     >
       <div className="space-y-6">
+        {flash?.success || flash?.error ? (
+          <MotionFade delay={0.05}>
+            <AdminFlash success={flash.success} error={flash.error} />
+          </MotionFade>
+        ) : null}
         {toolbar ? <MotionFade delay={0.05}>{toolbar}</MotionFade> : null}
         {children}
       </div>