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/src/util/git.ts

@@ -0,0 +1,35 @@
+import { Process } from "./process"
+
+export interface GitResult {
+  exitCode: number
+  text(): string
+  stdout: Buffer
+  stderr: Buffer
+}
+
+/**
+ * Run a git command.
+ *
+ * Uses Process helpers with stdin ignored to avoid protocol pipe inheritance
+ * issues in embedded/client environments.
+ */
+export async function git(args: string[], opts: { cwd: string; env?: Record<string, string> }): Promise<GitResult> {
+  return Process.run(["git", ...args], {
+    cwd: opts.cwd,
+    env: opts.env,
+    stdin: "ignore",
+    nothrow: true,
+  })
+    .then((result) => ({
+      exitCode: result.code,
+      text: () => result.stdout.toString(),
+      stdout: result.stdout,
+      stderr: result.stderr,
+    }))
+    .catch((error) => ({
+      exitCode: 1,
+      text: () => "",
+      stdout: Buffer.alloc(0),
+      stderr: Buffer.from(error instanceof Error ? error.message : String(error)),
+    }))
+}