feat(auth): restore Google sign-in and AI admin test routes

Google OAuth was implemented locally but never deployed; the login button
only renders when AUTH_GOOGLE_ID and AUTH_GOOGLE_SECRET are set. Also
restores /api/ai/test-* endpoints removed by mistake and wires Google
credentials into deploy workflows.

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/app/(admin)/admin/ai-test/ai-tester.tsx

@@ -51,10 +51,19 @@ export function AI_TESTER({ type }: { type: 'tags' | 'embeddings' | 'chat' }) {
     try {
       const response = await fetch(`/api/ai/test-${type}`, {
         method: 'POST',
-        headers: { 'Content-Type': 'application/json' }
+        headers: { 'Content-Type': 'application/json' },
       })
 
       const endTime = Date.now()
+      const contentType = response.headers.get('content-type') || ''
+      if (!contentType.includes('application/json')) {
+        const bodyPreview = (await response.text()).slice(0, 200)
+        throw new Error(
+          response.status === 404
+            ? `Route API introuvable (/api/ai/test-${type}). Redéployez l’application.`
+            : `Réponse non-JSON (HTTP ${response.status}): ${bodyPreview}`,
+        )
+      }
       const data = await response.json()
 
       setResult({