feat: agent version tracking, update button, device test, COM port list

- Migration 043: agent_version in workstations, netup device type
- agent-ws: sendCommandAndWait for async commands, save version on hello
- workstations route: list-ports, test-device, update, update-all endpoints
- agent-release route: GET /api/agents/latest-release reads latest.yml
- app.ts: serve /agent-updates/ static files
- api.ts: fix camelCase→snake_case for outgoing requests (fixes null:null)
- api.ts: new methods testDevice, sendUpdate, updateAll, listPorts
- EquipmentPage: version badge, update button, test (zap) button per device
- EquipmentPage: COM-port dropdown loaded from agent when online

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/routes/agent-release.ts

@@ -0,0 +1,23 @@
+import { FastifyPluginAsync } from 'fastify'
+import { readFile } from 'fs/promises'
+import { join } from 'path'
+
+const agentRelease: FastifyPluginAsync = async (fastify) => {
+  fastify.get('/api/agents/latest-release', { onRequest: [fastify.authenticate] }, async (_req, reply) => {
+    const updatesDir = process.env.AGENT_UPDATES_DIR ?? join(process.cwd(), '..', 'agent-updates')
+    try {
+      const yaml = await readFile(join(updatesDir, 'latest.yml'), 'utf8')
+      // Parse version: line like "version: 1.0.6"
+      const versionMatch = yaml.match(/^version:\s*(.+)$/m)
+      const pathMatch    = yaml.match(/^path:\s*(.+)$/m)
+      if (!versionMatch) return reply.code(404).send({ error: 'latest.yml not found or invalid' })
+      const version = versionMatch[1].trim()
+      const fileName = pathMatch?.[1].trim() ?? `HotelSync Agent Setup ${version}.exe`
+      return { version, fileName, downloadUrl: `/agent-updates/${encodeURIComponent(fileName)}` }
+    } catch {
+      return reply.code(404).send({ error: 'No release available' })
+    }
+  })
+}
+
+export default agentRelease