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/fixture.ts

@@ -0,0 +1,73 @@
+import { $ } from "bun"
+import * as fs from "fs/promises"
+import os from "os"
+import path from "path"
+import type { Config } from "../../src/config/config"
+
+// Strip null bytes from paths (defensive fix for CI environment issues)
+function sanitizePath(p: string): string {
+  return p.replace(/\0/g, "")
+}
+
+function exists(dir: string) {
+  return fs
+    .stat(dir)
+    .then(() => true)
+    .catch(() => false)
+}
+
+function clean(dir: string) {
+  return fs.rm(dir, {
+    recursive: true,
+    force: true,
+    maxRetries: 5,
+    retryDelay: 100,
+  })
+}
+
+async function stop(dir: string) {
+  if (!(await exists(dir))) return
+  await $`git fsmonitor--daemon stop`.cwd(dir).quiet().nothrow()
+}
+
+type TmpDirOptions<T> = {
+  git?: boolean
+  config?: Partial<Config.Info>
+  init?: (dir: string) => Promise<T>
+  dispose?: (dir: string) => Promise<T>
+}
+export async function tmpdir<T>(options?: TmpDirOptions<T>) {
+  const dirpath = sanitizePath(path.join(os.tmpdir(), "opencode-test-" + Math.random().toString(36).slice(2)))
+  await fs.mkdir(dirpath, { recursive: true })
+  if (options?.git) {
+    await $`git init`.cwd(dirpath).quiet()
+    await $`git config core.fsmonitor false`.cwd(dirpath).quiet()
+    await $`git config user.email "test@opencode.test"`.cwd(dirpath).quiet()
+    await $`git config user.name "Test"`.cwd(dirpath).quiet()
+    await $`git commit --allow-empty -m "root commit ${dirpath}"`.cwd(dirpath).quiet()
+  }
+  if (options?.config) {
+    await Bun.write(
+      path.join(dirpath, "opencode.json"),
+      JSON.stringify({
+        $schema: "https://opencode.ai/config.json",
+        ...options.config,
+      }),
+    )
+  }
+  const realpath = sanitizePath(await fs.realpath(dirpath))
+  const extra = await options?.init?.(realpath)
+  const result = {
+    [Symbol.asyncDispose]: async () => {
+      try {
+        await options?.dispose?.(realpath)
+      } finally {
+        if (options?.git) await stop(realpath).catch(() => undefined)
+        await clean(realpath).catch(() => undefined)
+      }
+    },
+    path: realpath,
+    extra: extra as T,
+  }
+  return result
+}