chore: update the xtermjs to v6 and fix session creation

[bajrangCoder]

• Updated the themes with new fields
• Added option to turn off the xtermjs scrollabr
• Fixed touch related stuff introduced in new version
• fix(terminal): wait for AXS server readiness before creating session

[greptile-apps]

Greptile Summary

This PR updates the terminal stack for xterm.js v6. The main changes are:

• xterm.js and related addons upgraded to v6-compatible versions.
• Terminal themes updated for the new selection and scrollbar theme fields.
• A setting added to show or hide the terminal scrollbar.
• Touch scrolling and selection adjusted for the new scrollbar behavior.
• Terminal startup and resize sync updated around AXS readiness and WebSocket reconnects.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• The scrollbar option now handles missing overview-ruler settings safely.
• The terminal resize path now forces a server sync when the WebSocket opens.

Important Files Changed

Filename	Overview
src/components/terminal/terminal.js	Adds scrollbar visibility handling, background updates, server readiness polling, and forced fit/resize sync.
src/settings/terminalSettings.js	Adds the showScrollbar setting and applies it to active terminals.
src/components/terminal/terminalManager.js	Updates terminal styling for xterm v6 scrollbar and viewport behavior.
src/components/terminal/terminalTouchScrolling.js	Moves touch scrolling to xterm public scrolling APIs for v6 compatibility.
src/components/terminal/terminalTouchSelection.js	Updates touch selection handling for xterm v6 scroll and resize events.
src/components/terminal/terminalThemeManager.js	Migrates terminal themes to xterm v6 field names and normalizes legacy plugin themes.

_{Reviews (4): Last reviewed commit: "fix(terminal): wait for AXS server readi..." | Re-trigger Greptile}

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