feat: add bun-fullstack agent and update skills

.opencode/skills/tech-stack/elysiajs/integrations/ai-sdk.md

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+# AI SDK Integration
+
+## What It Is
+Seamless integration with Vercel AI SDK via response streaming.
+
+## Response Streaming
+Return `ReadableStream` or `Response` directly:
+```typescript
+import { streamText } from 'ai'
+import { openai } from '@ai-sdk/openai'
+
+new Elysia().get('/', () => {
+  const stream = streamText({
+    model: openai('gpt-5'),
+    system: 'You are Yae Miko from Genshin Impact',
+    prompt: 'Hi! How are you doing?'
+  })
+  
+  return stream.textStream  // ReadableStream
+  // or
+  return stream.toUIMessageStream()  // UI Message Stream
+})
+```
+
+Elysia auto-handles stream.
+
+## Server-Sent Events
+Wrap `ReadableStream` with `sse`:
+```typescript
+import { sse } from 'elysia'
+
+.get('/', () => {
+  const stream = streamText({ /* ... */ })
+  
+  return sse(stream.textStream)
+  // or
+  return sse(stream.toUIMessageStream())
+})
+```
+
+Each chunk → SSE.
+
+## As Response
+Return stream directly (no Eden type safety):
+```typescript
+.get('/', () => {
+  const stream = streamText({ /* ... */ })
+  
+  return stream.toTextStreamResponse()
+  // or
+  return stream.toUIMessageStreamResponse()  // Uses SSE
+})
+```
+
+## Manual Streaming
+Generator function for control:
+```typescript
+import { sse } from 'elysia'
+
+.get('/', async function* () {
+  const stream = streamText({ /* ... */ })
+  
+  for await (const data of stream.textStream)
+    yield sse({ data, event: 'message' })
+  
+  yield sse({ event: 'done' })
+})
+```
+
+## Fetch for Unsupported Models
+Direct fetch with streaming proxy:
+```typescript
+.get('/', () => {
+  return fetch('https://api.openai.com/v1/chat/completions', {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      Authorization: `Bearer ${process.env.OPENAI_API_KEY}`
+    },
+    body: JSON.stringify({
+      model: 'gpt-5',
+      stream: true,
+      messages: [
+        { role: 'system', content: 'You are Yae Miko' },
+        { role: 'user', content: 'Hi! How are you doing?' }
+      ]
+    })
+  })
+})
+```
+
+Elysia auto-proxies fetch response with streaming.