security: fix critical auth gaps, SSRF, IDOR, and embedding error handling

CRITICAL:
- Add auth + admin check to 10 unprotected API routes (test-*, debug/*,
  config, models, fix-labels)
- Add CRON_SECRET bearer auth to /api/cron/reminders (was fully open)
- Add SSRF protection to getOllamaModels (blocks private/internal IPs)

HIGH:
- Fix getAllLabels() missing userId filter (leaked all users' labels)
- Fix /api/labels OR clause leaking other users' labels
- Fix IDOR in toggleAgent/getAgentActions (add ownership check)
- Fix getEmbeddings() returning [] on error in all 5 providers (corrupted
  semantic search with NaN cosine similarity) — now throws instead

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/app/api/ai/models/route.ts

@@ -1,5 +1,6 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { getSystemConfig } from '@/lib/config'
+import { auth } from '@/auth'
 
 // Modèles populaires pour chaque provider (2025)
 const PROVIDER_MODELS = {
@@ -41,6 +42,14 @@ const PROVIDER_MODELS = {
 }
 
 export async function GET(request: NextRequest) {
+  const session = await auth()
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
+  if ((session.user as any).role !== 'ADMIN') {
+    return NextResponse.json({ error: 'Forbidden' }, { status: 403 })
+  }
+
   try {
     const config = await getSystemConfig()
     const provider = (config.AI_PROVIDER || 'ollama').toLowerCase()