fix(settings): correct sidebar focus, settings panes, and icon sizing

[wzz6423]

Summary

• Restore distinct Editor and AI settings panes, including the external editor picker.
• Prevent duplicate sidebar group names and remove stale focus rings during rename, focus transfer, and window deactivation.
• Match the sidebar scrollbar to the tab-strip thumb without a visible track, keep alternate app icon previews normalized, and adapt group color fills to the active appearance.

GitHub Project

• Project: zshell Development

PR Type

• Type: fix

Validation

• Status: passed
• Command: make run; python3 mac/tests/test_workspace_hover.py; python3 mac/tests/test_sidebar_group_ordering.py; xcrun swiftc -parse mac/zshell/WorkspaceChromeViews.swift mac/zshell/AppKitProjectSidebarView.swift mac/zshell/ProjectGroup.swift mac/zshell/Settings/SettingsApplicationIconPicker.swift mac/zshell/Settings/SettingsEditorPane.swift; codesign --verify --deep --strict --verbose=2 'mac/build/debug/Build/Products/Debug/zshell Debug.app'
• Result: Debug build, code-signature verification, and both regression suites passed. Manual macOS checks covered group rename and duplicate rejection, Editor versus AI pane content, app icon selection, the sidebar scrollbar, and dark-mode group colors.

Risk and Rollback

• Risk: Sidebar drawing and settings layout changes affect AppKit presentation, while duplicate-name attempts now retain the existing group name.
• Rollback: Revert this pull request.

Related Issue

None

AI Attribution

• Agent: Codex
• Co-authored-by: Codex noreply@openai.com

[github-actions]

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• There is no unit test target: app changes are proven by building and running Zshell and exercising the change, so say in Validation what you did and attach screenshots or a recording for UI work. Run cargo test --locked in mac/Vendor/alacritty-bridge for bridge changes, bun run typecheck && bun run build in web/ for site changes, and bunx tsc --noEmit in mac/ for anything under mac/scripts/. Install dependencies with bun install --frozen-lockfile in each package before running Bun checks.

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