feat: admin paneli + blog + testimonials + SEO yöneticisi

Backend altyapısı:
- 4 yeni Appwrite tablosu: blog_posts, testimonials, seo_pages, seo_settings
- Appwrite Storage bucket: kovak-yazilim-media (görsel yüklemeleri)
- Appwrite Auth ile session cookie tabanlı koruma

Admin paneli (/admin):
- Login akışı (email/password) + protected layout
- Dashboard: sayım kartları + hızlı aksiyonlar
- Blog CRUD: markdown content, kapak görseli, draft/published, SEO alanları
- Services CRUD: lucide ikon seçici
- Projects CRUD: teknoloji etiketleri, live URL
- Testimonials CRUD: puanlama
- SEO yöneticisi: global ayarlar + sayfa bazlı override
- Mesaj inbox: status filtreleme + güncelleme
- Medya kütüphanesi: Appwrite Storage upload/delete

Public:
- /blog ve /blog/[slug] sayfaları (markdown render)
- Anasayfaya Testimonials bölümü
- Tüm public sayfalarda generateMetadata + seo_pages override
- Header'a Blog linki

Route yapısı:
- app/(site)/ — public site, Header/Footer ortak
- app/admin/login — auth dışı
- app/admin/(protected)/ — requireUser() korumalı

23 route üretiliyor, public static, admin dynamic.

app/admin/login/actions.ts

@@ -0,0 +1,46 @@
+"use server";
+
+import { cookies } from "next/headers";
+import { redirect } from "next/navigation";
+import { Account, Client } from "node-appwrite";
+import { SESSION_COOKIE } from "@/lib/auth";
+
+const endpoint = process.env.NEXT_PUBLIC_APPWRITE_ENDPOINT!;
+const projectId = process.env.NEXT_PUBLIC_APPWRITE_PROJECT_ID!;
+
+export type LoginState = { error?: string };
+
+export async function loginAction(
+  _prev: LoginState | undefined,
+  formData: FormData,
+): Promise<LoginState> {
+  const email = String(formData.get("email") ?? "").trim();
+  const password = String(formData.get("password") ?? "");
+
+  if (!email || !password) return { error: "E-posta ve şifre zorunlu" };
+
+  try {
+    const client = new Client().setEndpoint(endpoint).setProject(projectId);
+    const account = new Account(client);
+    const session = await account.createEmailPasswordSession({ email, password });
+    const store = await cookies();
+    store.set(SESSION_COOKIE, session.secret, {
+      httpOnly: true,
+      sameSite: "lax",
+      secure: process.env.NODE_ENV === "production",
+      path: "/",
+      expires: new Date(session.expire),
+    });
+  } catch (err) {
+    const msg = err instanceof Error ? err.message : "Giriş başarısız";
+    return { error: msg };
+  }
+
+  redirect("/admin");
+}
+
+export async function logoutAction() {
+  const store = await cookies();
+  store.delete(SESSION_COOKIE);
+  redirect("/admin/login");
+}