title_bar: Let the title bar own dragging and double clicking (#2667)

Double clicking the title bar zoomed the window even when the two clicks
were seconds apart, which is not what a double click should do.

## Cause

`WindowOptions::app_owns_titlebar_drag` was never set anywhere in this
repo, so it defaulted to `false`. GPUI documents that field as:

> Set this to `true` for windows that draw their own titlebar and move
the window themselves via `Window::start_window_move`. It marks the
whole content view as app-owned titlebar content, so AppKit neither
drags the window from the titlebar nor delays titlebar clicks while
disambiguating double-clicks (a delay first observed on macOS 27).

`TitleBar` is exactly that kind of title bar — it renders itself and
calls `start_window_move` — but never claimed the ownership. So on macOS
AppKit still treated the title bar as a system window-move region and
ran its own `AppleActionOnDoubleClick` handling in parallel with the
`on_double_click` handler in `TitleBar`. The zoom came from the system
path, which is why it could not be fixed from inside the component.

## Changes

- Add `TitleBar::window_options()`, the window options counterpart of
the existing `title_bar_options()`. It sets both `titlebar` and
`app_owns_titlebar_drag`, so a window that renders a `TitleBar` gets
this right by just using it as the base of its `WindowOptions`.
- Use it in the stories and all examples that render a `TitleBar`.
- `tiles.rs` had an inlined copy of `title_bar_options()`; it now shares
the same base.
- Drop the `#[cfg(not(target_os = "linux"))]` on the `titlebar` field in
`dock.rs`. `appears_transparent` is only read by the macOS and Windows
backends, so the cfg produced no behavior difference.
- Document both the recommended `window_options()` and the manual
`app_owns_titlebar_drag` setup, in English and Chinese.

## Testing

Verified on macOS (Darwin 27): two clicks a few seconds apart no longer
zoom the window, and a real double click still zooms.

AI generated: the patch was written with Claude Code and reviewed by me.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>