feat: add start/stop/restart buttons for VMs and LXCs

- New POST /api/power route for Proxmox power operations
- powerControl() method in proxmox.js library
- Start/Stop/Restart action buttons in VMList and LXCList tables
- Status feedback banner in Dashboard on power action

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

src/app/api/power/route.js

@@ -0,0 +1,28 @@
+import { NextResponse } from 'next/server';
+import { powerControl } from '@/lib/proxmox';
+
+/**
+ * @param {import('next').Request} req
+ */
+export async function POST(req) {
+  try {
+    const { node, vmid, type, action } = await req.json();
+
+    if (!node || !vmid || !type || !action) {
+      return NextResponse.json({ error: 'Missing required fields' }, { status: 400 });
+    }
+
+    if (!['qemu', 'lxc'].includes(type)) {
+      return NextResponse.json({ error: 'Invalid type, must be qemu or lxc' }, { status: 400 });
+    }
+
+    if (!['start', 'stop', 'restart'].includes(action)) {
+      return NextResponse.json({ error: 'Invalid action, must be start, stop, or restart' }, { status: 400 });
+    }
+
+    await powerControl(node, vmid, type, action);
+    return NextResponse.json({ ok: true, timestamp: Date.now() });
+  } catch (error) {
+    return NextResponse.json({ error: error.message, ok: false }, { status: 502 });
+  }
+}