Add available commands to --help output

The bootstrap argparse help was missing any mention of subcommands.
Added an epilog listing auth, projects, and tui commands with
descriptions, and noting that the default (no args) launches the TUI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: shuveb

src/mfbt/__main__.py

@@ -18,9 +18,20 @@ def get_version() -> str:
 
 def build_parser() -> argparse.ArgumentParser:
     """Build the bootstrap argument parser."""
+    epilog = """\
+commands:
+  (none)              Launch interactive TUI (default)
+  auth                Authentication commands (login, status, refresh, logout)
+  projects            Manage projects (list, show, create, switch, archive, delete)
+  tui                 Launch interactive TUI
+
+Run 'mfbt <command> --help' for details on a specific command.
+"""
     parser = argparse.ArgumentParser(
         prog="mfbt",
         description="CLI tool for the mfbt platform",
+        epilog=epilog,
+        formatter_class=argparse.RawDescriptionHelpFormatter,
     )
     parser.add_argument(
         "--version",