fix: Polish message editor, settings dialog and minor UX tweaks

[charlesvien]

Problem

Small UI inconsistencies across the message editor, settings dialog and session indicator.

Changes

1. Refine message editor padding, spacing and add slim custom scrollbar
2. Style hyperlinks in Tiptap editor with accent color and underline
3. Change "interrupt" to "stop" in generating indicator copy
4. Use text cursor for inline editable textarea
5. Make settings scroll area span full panel width with centered content

How did you test this?

Manually

[charlesvien]

• fix: Show parent directory in file mention chips #1472
• fix: Fix Enter key blocked after dismissing empty suggestion popup #1471
• fix: Open active file in external app instead of repo directory #1470
• fix: Rename bypass permissions to auto-accept permissions #1469
• fix: Polish message editor, settings dialog and minor UX tweaks #1468 👈 (View in Graphite)
• main

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[charlesvien]

Merge activity

• Apr 3, 1:05 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Apr 3, 1:05 AM UTC: @charlesvien merged this pull request with Graphite.