feat(agent): v0.3.5 Windows inbound forwarding, UI actions, lifecycle

- Configure tailscale serve automatically for each instance on Windows userspace networking.
- Add local UI buttons: start/stop/reset/delete instances (stop/start preserve volumes).
- Clean shutdown: stop tailscaled and instances, notify server with instance_stopped.
- Restart tailscaled on agent boot using persisted state when pre-auth key is absent.
- Sync instance stopped/deleted status to dashboard (server/lib/websocket.ts).
- Security: include prior authz/scoping changes across API routes, ephemeral pre-auth keys, ACL policy, internal API key.
- Update SUIVI_VPN_ONDEMAND.md and docs/ONBOARDING_CLIENT.md.
- Bump agent version to 0.3.5.

server/app/api/internal/send-to-node/route.ts

@@ -1,7 +1,22 @@
 import { NextRequest, NextResponse } from "next/server";
 import { sendToNode } from "@/lib/websocket";
 
+function getBearerToken(req: NextRequest): string | null {
+  const auth = req.headers.get("authorization") || "";
+  const match = auth.match(/^Bearer\s+(\S+)$/i);
+  return match ? match[1] : null;
+}
+
 export async function POST(req: NextRequest) {
+  const apiKey = process.env.INTERNAL_API_KEY;
+  if (!apiKey) {
+    return NextResponse.json({ error: "Internal API key not configured" }, { status: 500 });
+  }
+  const token = getBearerToken(req);
+  if (!token || token !== apiKey) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
   const body = await req.json();
   const { nodeId, message } = body;
   if (!nodeId || !message) {