fix(security): Phase 1 P0 hardening from cross-project audit

Close open uploads, image-proxy SSRF, fail-open AI quotas in production,
auth gaps on app routes, and MCP tenant isolation issues.

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

memento-note/app/api/image-proxy/route.ts

@@ -1,6 +1,13 @@
 import { NextRequest, NextResponse } from 'next/server'
+import { auth } from '@/auth'
+import { isBlockedFetchHost } from '@/lib/ssrf-guard'
 
 export async function GET(req: NextRequest) {
+  const session = await auth()
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
+
   const url = req.nextUrl.searchParams.get('url')
   if (!url) return NextResponse.json({ error: 'Missing url' }, { status: 400 })
 
@@ -9,6 +16,9 @@ export async function GET(req: NextRequest) {
     if (!['http:', 'https:'].includes(parsed.protocol)) {
       return NextResponse.json({ error: 'Invalid protocol' }, { status: 400 })
     }
+    if (isBlockedFetchHost(parsed.hostname)) {
+      return NextResponse.json({ error: 'Host not allowed' }, { status: 403 })
+    }
 
     const controller = new AbortController()
     const timeout = setTimeout(() => controller.abort(), 5000)