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.

lib/app-config.ts

@@ -24,16 +24,6 @@ export {
   type MailSettings,
   type MailSettingsFormValues,
 } from "./mail-settings";
-export {
-  CONTACT_PROTECTION_SETTINGS_KEY,
-  buildDefaultContactProtectionSettings,
-  parseContactProtectionValue,
-  toContactProtectionFormValues,
-  toPublicContactProtectionSettings,
-  type ContactProtectionSettings,
-  type ContactProtectionFormValues,
-  type PublicContactProtectionSettings,
-} from "./contact-protection";
 export {
   MARQUEE_SETTINGS_KEY,
   buildDefaultMarqueeSettings,
@@ -67,16 +57,6 @@ import {
   type MailSettings,
   type MailSettingsFormValues,
 } from "./mail-settings";
-import {
-  CONTACT_PROTECTION_SETTINGS_KEY,
-  buildDefaultContactProtectionSettings,
-  parseContactProtectionValue,
-  toContactProtectionFormValues,
-  toPublicContactProtectionSettings,
-  type ContactProtectionSettings,
-  type ContactProtectionFormValues,
-  type PublicContactProtectionSettings,
-} from "./contact-protection";
 import {
   MARQUEE_SETTINGS_KEY,
   buildDefaultMarqueeSettings,
@@ -179,46 +159,6 @@ export async function updateMailSettings(settings: MailSettings): Promise<void>
   });
 }
 
-export async function getContactProtectionSettings(): Promise<ContactProtectionSettings> {
-  try {
-    const config = await prisma.appConfig.findUnique({
-      where: { key: CONTACT_PROTECTION_SETTINGS_KEY },
-      select: { value: true },
-    });
-
-    return parseContactProtectionValue(config?.value);
-  } catch {
-    return buildDefaultContactProtectionSettings();
-  }
-}
-
-export async function getContactProtectionFormValues(): Promise<ContactProtectionFormValues> {
-  const settings = await getContactProtectionSettings();
-
-  return toContactProtectionFormValues(settings);
-}
-
-export async function getPublicContactProtectionSettings(): Promise<PublicContactProtectionSettings> {
-  const settings = await getContactProtectionSettings();
-
-  return toPublicContactProtectionSettings(settings);
-}
-
-export async function updateContactProtectionSettings(
-  settings: ContactProtectionSettings,
-): Promise<void> {
-  await prisma.appConfig.upsert({
-    where: { key: CONTACT_PROTECTION_SETTINGS_KEY },
-    update: {
-      value: JSON.stringify(settings),
-    },
-    create: {
-      key: CONTACT_PROTECTION_SETTINGS_KEY,
-      value: JSON.stringify(settings),
-    },
-  });
-}
-
 export async function getMarqueeSettings(): Promise<MarqueeSettings> {
   try {
     const config = await prisma.appConfig.findUnique({