feat: bootstrap vela UI and gateway workspace

Establish the monorepo, tooling, and starter apps so UI and gateway development can begin from a documented, runnable baseline.

apps/vela-gateway/README.md

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+# vela-gateway
+
+This workspace contains the Vela gateway service as a minimal Fastify app.
+
+Current status:
+
+- Fastify server boots in the Yarn workspace
+- `/` and `/health` endpoints provide a runnable service baseline
+- WebSocket session orchestration remains a later increment

apps/vela-gateway/package.json

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+{
+  "name": "vela-gateway",
+  "private": true,
+  "version": "0.0.0",
+  "description": "Minimal Fastify app for the Vela gateway service.",
+  "scripts": {
+    "dev": "node --watch src/index.js",
+    "start": "node src/index.js",
+    "build": "node -e \"console.log('vela-gateway: no build step required')\""
+  },
+  "dependencies": {
+    "fastify": "^5.2.1"
+  }
+}

apps/vela-gateway/src/index.js

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+const Fastify = require('fastify');
+
+function buildServer() {
+	const app = Fastify({ logger: true });
+
+	app.get('/', async () => ({
+		service: 'vela-gateway',
+		status: 'ok',
+		transport: 'http',
+		next: 'websocket session skeleton'
+	}));
+
+	app.get('/health', async () => ({ status: 'ok' }));
+
+	return app;
+}
+
+async function start() {
+	const app = buildServer();
+	const port = Number(process.env.PORT ?? 3001);
+	const host = process.env.HOST ?? '0.0.0.0';
+
+	try {
+		await app.listen({ port, host });
+	} catch (error) {
+		app.log.error(error);
+		process.exit(1);
+	}
+}
+
+if (require.main === module) {
+	start();
+}
+
+module.exports = {
+	buildServer
+};