feat(tabs): close document tabs with middle mouse click

[Kechos23]

Summary

Allow the middle mouse button to close a document tab, matching familiar browser-tab behavior.

• Reuse the existing close-tab operation: closing does not delete the workspace document or its draft.
• Close inactive tabs without activating them first.
• Handle clicks on the tab title and nested controls, and prevent middle-button autoscroll within tabs.
• Keep left-click activation and right-click context menus unchanged.

This uses shared application code for web and desktop and is independent of the linked-workspace PR. It requires no runtime changes.

Validation

• 19 Chromium tests passed: two focused middle-click regressions and the 17 existing tab/split/sidebar regressions.
• Standard desktop resources regenerated and a review EXE built with the official pinned Neutralino runtime.
• The upstream diff contains only script.js, its generated desktop copy, and the focused test file.
• Firefox/WebKit and native manual testing of this exact review EXE were not run.

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Project	Deployment	Actions	Updated
markdown-viwer	Ready	Preview	Oct 5, 2026 4:24pm UTC

[ThisIs-Developer]

@Kechos23 really nice UX improvement. Middle-click tab closing feels natural and makes tab handling faster. Thanks for adding this! 🙌