feat(auth): Google ile Giriş + landing/login + çalışan çıkış + admin rolü

- server/auth.mjs: ID token'ı oauth2.googleapis.com/tokeninfo ile doğrula (ek bağımlılık yok), HMAC imzalı app token, ADMIN_EMAILS ile admin
- POST /api/auth/google, GET /api/auth/google/config, GET /api/auth/me
- LoginPage: GIS butonlu landing/giriş; giriş yapılmadan uygulama açılmaz
- Header çıkış butonu artık çalışıyor; kullanıcı adı/avatar Google'dan
- AI Model Ayarları sekmesi sadece admin'e görünür
- Env: GOOGLE_CLIENT_ID + ADMIN_EMAILS (Coolify'dan)

src/context/AppContext.jsx

@@ -2,6 +2,7 @@ import React, { createContext, useContext, useState, useEffect } from 'react';
 import { MOCK_TENDERS, MOCK_LIVE_STATS, MOCK_COMPANY_STATS } from '../data/mockTenders';
 import { parseWebsiteCapabilitiesDynamically } from '../services/webScraperService';
 import { fetchLiveTenders, fetchTenderDetail, mergeUserState } from '../services/tenderApi';
+import { restoreSession, clearSession, getStoredUser } from '../services/auth';
 
 const AppContext = createContext();
 
@@ -34,6 +35,24 @@ export const AppProvider = ({ children }) => {
   const [liveDataError, setLiveDataError] = useState(null);
   const [liveDataSource, setLiveDataSource] = useState(null);
 
+  // --- Kimlik doğrulama (Google ile Giriş) ---
+  const [authUser, setAuthUser] = useState(() => getStoredUser());
+  const [authReady, setAuthReady] = useState(false);
+  const isAuthenticated = Boolean(authUser);
+  const isAdmin = Boolean(authUser?.isAdmin);
+
+  useEffect(() => {
+    restoreSession()
+      .then((u) => setAuthUser(u))
+      .finally(() => setAuthReady(true));
+  }, []);
+
+  const handleLogin = (user) => setAuthUser(user);
+  const handleLogout = () => {
+    clearSession();
+    setAuthUser(null);
+  };
+
   // Canlı ihale verisini (ilan.gov.tr) çeker; kullanıcının kanban/takip durumunu korur.
   const refreshLiveEKAPData = async ({ refresh = true } = {}) => {
     setIsRefreshingLive(true);
@@ -338,6 +357,12 @@ export const AppProvider = ({ children }) => {
       refreshLiveEKAPData,
       liveDataError,
       liveDataSource,
+      authUser,
+      authReady,
+      isAuthenticated,
+      isAdmin,
+      handleLogin,
+      handleLogout,
       liveStats,
       searchQuery,
       setSearchQuery,