AppShell: undecorated mode lost window controls + chrome dragging

[israel-dryer]

Summary

A user demonstrated that AppShell(undecorated=True) no longer provides window controls (minimize / maximize / close) or chrome-row dragging. In undecorated mode the OS title bar is removed and a custom border is drawn, but there is now no way to move, minimize, maximize, or close the window from the chrome — leaving the window effectively stuck.

Root cause

The clean-slate Shell rewrite (shipped in 0.1.0a10, PRs #133–#136) builds its chrome band from a plain Frame:

# src/bootstack/widgets/_impl/composites/shell/layout.py
self._chrome = Frame(root, surface=self._chrome_surface)

The previous region-based AppShell got this behavior for free from the internal Toolbar, which supports show_window_controls= and draggable= (and auto-enables drag with controls):

# src/bootstack/widgets/_impl/composites/toolbar.py
self._draggable = draggable or show_window_controls  # Auto-enable drag with window controls
... self.bind('<B1-Motion>', self._on_drag_motion, add='+')

The new chrome Frame carries none of that. The docstring at layout.py:77 still claims undecorated "Enables window controls + dragging on the chrome row" — which is now inaccurate.

Proposed direction (enrich AppShell)

• In undecorated mode, render window-control buttons (minimize / maximize / close) at the right edge of the chrome row.
• Make the chrome row draggable to move the window (and ideally double-click-to-maximize), reusing the existing _on_drag_motion-style logic.
• Expose options on AppShell/App to configure this — e.g. which controls show, whether the chrome is draggable — rather than hardwiring. Decide whether this lives on the public App/AppShell chrome surface or a dedicated window-controls config.
• macOS: overrideredirect is already force-disabled there; keep custom controls Windows/Linux-only (ties into the separate native-macOS-chrome follow-up).
• Fix the layout.py:77 docstring once behavior is restored.

Acceptance

• AppShell(undecorated=True) shows working min/max/close and can be dragged by its chrome row on Windows/Linux.
• The behavior is configurable via documented public options.