feat(cli): add argument parser and TTY detection

- New CLI argument parser supporting subcommands, short/long flags,
  flag values, positional args, aliases, and --help per command
- TTY detection via fstatSync (Bun compat: process.stdin.isTTY is
  undefined in Bun 1.3.x)
- Extended types: CommitResult, StreamCallbacks

src/tty.ts

@@ -0,0 +1,36 @@
+// TTY detection for Bun compatibility.
+// Bun does not set process.stdin.isTTY, so we use fs.fstatSync.
+
+import { fstatSync } from "node:fs";
+
+let _stdinTTY: boolean | null = null;
+
+export function initTTY(): void {
+  if (_stdinTTY !== null) return;
+
+  try {
+    // fd 0 = stdin. On Unix, a TTY is a character device.
+    const stat = fstatSync(0);
+    _stdinTTY = stat.isCharacterDevice();
+  } catch {
+    _stdinTTY = false;
+  }
+}
+
+export function isStdinTTY(): boolean {
+  if (_stdinTTY === null) initTTY();
+  return _stdinTTY!;
+}
+
+export function isStdoutTTY(): boolean {
+  // Use a heuristic for stdout — check if we're in a terminal
+  if (process.env.TERM || process.env.TERM_PROGRAM) return true;
+  if (process.env.NO_COLOR) return false;
+  // Try fstat on fd 1 (stdout)
+  try {
+    const stat = fstatSync(1);
+    return stat.isCharacterDevice();
+  } catch {
+    return false;
+  }
+}