Enhancement: Add "Close Others", "Close Left", "Close Right" to chat tab context menu

[mabry1985]

Problem

The chat tab bar context menu currently only has basic options (close tab, maybe pin). With many open tabs, closing them individually is tedious.

Proposal

Add bulk-close actions to the tab context menu, matching common browser patterns:

• Close Other Tabs — close all tabs except the one right-clicked
• Close Tabs to the Left — close all tabs to the left of the selected tab
• Close Tabs to the Right — close all tabs to the right of the selected tab
• (optional) Close All Tabs — close every tab

Notes

• Should respect pinned tabs (skip them, or require unpinning first)
• Match the positioning/behavior of browser tab context menus for familiarity

[mabry1985]

Shipped in #2112 (merged). Closing — the PR predates the closing-keyword convention in the team's briefs.