refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

packages/tfcode/test/fixture/skills/agents-sdk/references/callable.md

@@ -0,0 +1,92 @@
+# Callable Methods
+
+Fetch `docs/callable-methods.md` from `https://github.com/cloudflare/agents/tree/main/docs` for complete documentation.
+
+## Overview
+
+`@callable()` exposes agent methods to clients via WebSocket RPC.
+
+```typescript
+import { Agent, callable } from "agents"
+
+export class MyAgent extends Agent<Env, State> {
+  @callable()
+  async greet(name: string): Promise<string> {
+    return `Hello, ${name}!`
+  }
+
+  @callable()
+  async processData(data: unknown): Promise<Result> {
+    // Long-running work
+    return result
+  }
+}
+```
+
+## Client Usage
+
+```typescript
+// Basic call
+const greeting = await agent.call("greet", ["World"])
+
+// With timeout
+const result = await agent.call("processData", [data], {
+  timeout: 5000, // 5 second timeout
+})
+```
+
+## Streaming Responses
+
+```typescript
+import { Agent, callable, StreamingResponse } from "agents"
+
+export class MyAgent extends Agent<Env, State> {
+  @callable({ streaming: true })
+  async streamResults(stream: StreamingResponse, query: string) {
+    for await (const item of fetchResults(query)) {
+      stream.send(JSON.stringify(item))
+    }
+    stream.close()
+  }
+
+  @callable({ streaming: true })
+  async streamWithError(stream: StreamingResponse) {
+    try {
+      // ... work
+    } catch (error) {
+      stream.error(error.message) // Signal error to client
+      return
+    }
+    stream.close()
+  }
+}
+```
+
+Client with streaming:
+
+```typescript
+await agent.call("streamResults", ["search term"], {
+  stream: {
+    onChunk: (data) => console.log("Chunk:", data),
+    onDone: () => console.log("Complete"),
+    onError: (error) => console.error("Error:", error),
+  },
+})
+```
+
+## Introspection
+
+```typescript
+// Get list of callable methods on an agent
+const methods = await agent.call("getCallableMethods", [])
+// Returns: ["greet", "processData", "streamResults", ...]
+```
+
+## When to Use
+
+| Scenario                             | Use                         |
+| ------------------------------------ | --------------------------- |
+| Browser/mobile calling agent         | `@callable()`               |
+| External service calling agent       | `@callable()`               |
+| Worker calling agent (same codebase) | DO RPC directly             |
+| Agent calling another agent          | `getAgentByName()` + DO RPC |