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.

app/_admin/portfolio/actions.ts

@@ -8,6 +8,7 @@ import { ZodError } from "zod";
 
 import { routing } from "@/i18n/routing";
 import { getAdminAppPath, toInternalAdminPath } from "@/lib/admin-routing";
+import { withFlash } from "@/lib/admin-feedback";
 import { clearAdminSessionCookie, isAdminAuthenticated } from "@/lib/admin-auth";
 import { deleteEntityMediaUsages, replaceEntityMediaUsages } from "@/lib/media";
 import { resolveMediaSelection } from "@/lib/media-service";
@@ -35,12 +36,6 @@ function getRedirectPath(formData: FormData, fallbackPath: string) {
   return String(formData.get("redirectPath") ?? fallbackPath);
 }
 
-function withMessage(pathname: string, type: "success" | "error", message: string) {
-  const params = new URLSearchParams();
-  params.set(type, message);
-
-  return `${pathname}?${params.toString()}`;
-}
 
 function normalizeCheckboxValue(formData: FormData, key: string) {
   return isCheckedFormValue(formData.get(key));
@@ -139,7 +134,7 @@ export async function upsertCategoryAction(formData: FormData) {
     }
 
     await revalidatePortfolioPages();
-    redirect(withMessage(redirectPath, "success", "Kategorie gespeichert."));
+    redirect(withFlash(redirectPath, { success: "Kategorie gespeichert." }));
   } catch (error) {
     if (isRedirectError(error)) {
       throw error;
@@ -152,7 +147,7 @@ export async function upsertCategoryAction(formData: FormData) {
           ? "Kategorie Slug muss eindeutig sein."
           : "Kategorie konnte nicht gespeichert werden.";
 
-    redirect(withMessage(redirectPath, "error", message));
+    redirect(withFlash(redirectPath, { error: message }));
   }
 }
 
@@ -170,7 +165,7 @@ export async function deleteCategoryAction(formData: FormData) {
     });
 
     if (projectCount > 0) {
-      redirect(withMessage(redirectPath, "error", "Kategorie mit Projekten kann nicht geloescht werden."));
+      redirect(withFlash(redirectPath, { error: "Kategorie mit Projekten kann nicht geloescht werden." }));
     }
 
     await prisma.category.delete({
@@ -180,13 +175,13 @@ export async function deleteCategoryAction(formData: FormData) {
     });
 
     await revalidatePortfolioPages();
-    redirect(withMessage(redirectPath, "success", "Kategorie geloescht."));
+    redirect(withFlash(redirectPath, { success: "Kategorie geloescht." }));
   } catch (error) {
     if (isRedirectError(error)) {
       throw error;
     }
 
-    redirect(withMessage(redirectPath, "error", "Kategorie konnte nicht geloescht werden."));
+    redirect(withFlash(redirectPath, { error: "Kategorie konnte nicht geloescht werden." }));
   }
 }
 
@@ -529,7 +524,9 @@ export async function saveProjectAction(formData: FormData) {
     }
 
     redirect(
-      withMessage(getAdminAppPath(`/portfolio/projects/${projectResult.project.id}`), "success", "Projekt gespeichert."),
+      withFlash(getAdminAppPath(`/portfolio/projects/${projectResult.project.id}`), {
+        success: "Projekt gespeichert.",
+      }),
     );
   } catch (error) {
     if (isRedirectError(error)) {
@@ -562,7 +559,7 @@ export async function saveProjectAction(formData: FormData) {
         },
       });
     }
-    redirect(withMessage(redirectPath, "error", message));
+    redirect(withFlash(redirectPath, { error: message }));
   }
 }
 
@@ -582,7 +579,7 @@ export async function deleteProjectAction(formData: FormData) {
     });
 
     if (!project) {
-      redirect(withMessage(getAdminAppPath("/portfolio"), "error", "Projekt nicht gefunden."));
+      redirect(withFlash(getAdminAppPath("/portfolio"), { error: "Projekt nicht gefunden." }));
     }
 
     await prisma.portfolioProject.delete({
@@ -600,12 +597,12 @@ export async function deleteProjectAction(formData: FormData) {
       revalidatePath(getLocalizedPath(locale, `/portfolio/${project.slug}`, siteSettings.defaultLocale));
     }
 
-    redirect(withMessage(getAdminAppPath("/portfolio"), "success", "Project deleted."));
+    redirect(withFlash(getAdminAppPath("/portfolio"), { success: "Projekt geloescht." }));
   } catch (error) {
     if (isRedirectError(error)) {
       throw error;
     }
 
-    redirect(withMessage(getAdminAppPath("/portfolio"), "error", "Unable to delete project."));
+    redirect(withFlash(getAdminAppPath("/portfolio"), { error: "Projekt konnte nicht geloescht werden." }));
   }
 }