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/theme-toggle.tsx

@@ -5,14 +5,11 @@ import { useTheme } from "next-themes";
 import { useEffect, useState } from "react";
 import { useSound } from "@/components/sound-provider";
 import { Button, type ButtonProps } from "@/components/ui/button";
-import { toast } from "@/lib/toast";
 import { cn } from "@/lib/utils";
 
 type ThemeToggleProps = {
   ariaLabel?: string;
   label?: string;
-  lightToastLabel?: string;
-  darkToastLabel?: string;
   variant?: ButtonProps["variant"];
   className?: string;
   iconClassName?: string;
@@ -21,8 +18,6 @@ type ThemeToggleProps = {
 export function ThemeToggle({
   ariaLabel = "Toggle theme",
   label,
-  lightToastLabel = "Light mode enabled",
-  darkToastLabel = "Dark mode enabled",
   variant = "outline",
   className,
   iconClassName,
@@ -58,7 +53,6 @@ export function ThemeToggle({
 
     setTheme(nextTheme);
     playSound(nextTheme === "dark" ? "/audio/dark.mp3" : "/audio/light.mp3");
-    toast(nextTheme === "dark" ? darkToastLabel : lightToastLabel);
   };
 
   return (