feat: add bun-fullstack agent and update skills

.agent/skills/tech-stack/elysiajs/integrations/astro.md

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+# Astro Integration - SKILLS.md
+
+## What It Is
+Run Elysia on Astro via Astro Endpoint.
+
+## Setup
+1. Set output to server:
+```javascript
+// astro.config.mjs
+export default defineConfig({
+  output: 'server'
+})
+```
+
+2. Create `pages/[...slugs].ts`
+3. Define Elysia server + export handlers:
+```typescript
+// pages/[...slugs].ts
+import { Elysia, t } from 'elysia'
+
+const app = new Elysia()
+  .get('/api', () => 'hi')
+  .post('/api', ({ body }) => body, {
+    body: t.Object({ name: t.String() })
+  })
+
+const handle = ({ request }: { request: Request }) => app.handle(request)
+
+export const GET = handle
+export const POST = handle
+```
+
+WinterCG compliance - works normally.
+
+Recommended: Run Astro on Bun (Elysia designed for Bun).
+
+## Prefix for Non-Root
+If placed in `pages/api/[...slugs].ts`, set prefix:
+```typescript
+// pages/api/[...slugs].ts
+const app = new Elysia({ prefix: '/api' })
+  .get('/', () => 'hi')
+
+const handle = ({ request }: { request: Request }) => app.handle(request)
+
+export const GET = handle
+export const POST = handle
+```
+
+Ensures routing works in any location.
+
+## Benefits
+Co-location of frontend + backend. End-to-end type safety with Eden.
+
+## pnpm
+Manual install:
+```bash
+pnpm add @sinclair/typebox openapi-types
+```