fix: suppress browser context menu and prevent trackpad tap from dism…

[aaradhyaberisfdc]

Problem

When using ttyd with tmux (set -g mouse on), right-clicking to open tmux's context menu has two issues:

1. Mac trackpad tap dismisses menu instantly: a two-finger tap generates mousedown+mouseup within ~100ms. xterm.js sends the button release as an SGR mouse report, and tmux closes its menu immediately.
2. Browser context menu overlaps tmux's menu: the native browser menu appears on top, interfering with the application menu.

Additionally, no-button motion events (code & 3 === 3) sent after the release tell tmux "no button is held", which also dismisses the menu.

Fix

Three-layer interception:

1. contextmenu handler: suppresses the browser menu during mouse tracking. Shift+right-click bypasses to show the browser's native menu.
2. mouseup capture handler: blocks the right-button release at document level before xterm.js can generate a report.
3. onData SGR filter: drops right-button release and no-button motion reports while the filter is active. Resets on non-right-button press (user selecting a menu item) or after a safety timeout.

All three are no-ops when mouse tracking is off (normal shell usage).

Testing

With set -g mouse on in tmux:

• Right-click opens tmux menu and it stays open
• Click a menu item to select it — works normally
• Shift+right-click shows browser's native context menu
• Regular terminal usage (no tmux) is unaffected