feat(codemirror): shift + click selection

[Autist1Coder]

Closes: #1897

Recording.at.February25-084554am.3.mp4

[greptile-apps]

Greptile Summary

This PR implements shift+click selection functionality for the CodeMirror editor by adding a custom DOM event handler extension.

The implementation captures the selection anchor on pointerup when shift is pressed (either via event.shiftKey or the quickTools shift button at quickTools.$footer.dataset.shift), then extends the selection on the subsequent click event. The extension uses pointer ID mapping to track individual pointers and includes automatic cleanup via a 1001ms timeout to prevent memory leaks from stale entries.

Key changes:

• Imports EditorSelection from @codemirror/state
• Adds shiftClickSelectionExtension with pointerup and click handlers
• Uses pointer ID mapping to associate pointerup events with click events
• Includes safety checks for trusted and primary pointer events only
• Integrated into editor initialization in two locations (lines 764 and 1128)

Confidence Score: 4/5

• This PR is safe to merge with low risk - implements a focused bug fix for shift+click selection
• The change is a targeted fix that adds missing shift+click selection functionality. The implementation follows CodeMirror patterns, includes appropriate safety checks (trusted/primary events), and has cleanup mechanisms. Minor confidence reduction due to the complexity of event timing between pointerup and click handlers, though the approach appears sound based on the codebase patterns.
• No files require special attention

Important Files Changed

Filename	Overview
src/lib/editorManager.js	Added shift+click selection extension with pointer event handling to extend selections, includes timeout-based cleanup mechanism

_{Last reviewed commit: f205140}

[bajrangCoder]

Also add a editor setting to toggle this behaviour