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/site-header.tsx

@@ -15,7 +15,6 @@ import { ThemeToggle } from "@/components/theme-toggle";
 import { Button } from "@/components/ui/button";
 import { buildAdminUrl } from "@/lib/admin-routing";
 import { getLocalizedPath, stripLocalePrefix } from "@/lib/locale";
-import { toast } from "@/lib/toast";
 import { cn } from "@/lib/utils";
 
 const navItems = [
@@ -211,7 +210,6 @@ export function SiteHeader({
 
     logoClickTimesRef.current = [];
     event.preventDefault();
-    toast(t("logoTripleClick"));
   };
 
   return (
@@ -317,15 +315,11 @@ export function SiteHeader({
               <SoundToggle
                 ariaLabel={t("soundMute")}
                 mutedAriaLabel={t("soundUnmute")}
-                mutedToastLabel={t("soundMuted")}
-                unmutedToastLabel={t("soundEnabled")}
                 variant="ghost"
                 className={desktopControlButtonClassName}
               />
               <ThemeToggle
                 ariaLabel={t("themeToggle")}
-                lightToastLabel={t("themeLight")}
-                darkToastLabel={t("themeDark")}
                 variant="ghost"
                 className={desktopControlButtonClassName}
               />
@@ -467,15 +461,11 @@ export function SiteHeader({
                       <SoundToggle
                         ariaLabel={t("soundMute")}
                         mutedAriaLabel={t("soundUnmute")}
-                        mutedToastLabel={t("soundMuted")}
-                        unmutedToastLabel={t("soundEnabled")}
                         variant="ghost"
                         className={mobileControlButtonClassName}
                       />
                       <ThemeToggle
                         ariaLabel={t("themeToggle")}
-                        lightToastLabel={t("themeLight")}
-                        darkToastLabel={t("themeDark")}
                         variant="ghost"
                         className={mobileControlButtonClassName}
                       />