feat: group worktrees by name across repos with rename support

[malaporte]

Summary

Adds a new view mode that groups worktrees from multiple repositories when they share the same directory name, making it easy to see related work across repos at a glance. Also adds the ability to rename worktrees (move their directory on disk via git worktree move).

Changes

• View toggle: SegmentedControl in the header switches between "Repos" (existing) and "Names" (new grouped view)
• NameGroupDashboard: New component that collects worktrees from all repos, groups them by directory name, and renders collapsible sections
• Repo badge on cards: In the name-grouped view, each card shows a gray badge with the repo name for easy identification
• Rename worktree: New pencil icon on worktree cards opens a modal to rename the worktree directory (git worktree move)
• Backend: New renameWorktree service function and git:renameWorktree RPC channel

Testing

• All 68 existing tests pass with the new viewMode and onRenamed props added to test fixtures
• Typecheck passes cleanly
• Manual verification: toggle between views, search filtering works in both modes, rename validates input (no slashes, non-empty, must differ from current)

Reviewer Notes

• The name-grouped view uses invisible RepoLoader sub-components (one per repo) to call useWorktrees since React hooks can't be called dynamically. Data flows up via callbacks to the parent which computes the groups.
• Drag-and-drop reordering only applies to the Repos view (not meaningful for auto-grouped names).
• View mode state is ephemeral (resets on app restart). Can be persisted in AppConfig later if desired.

[github-actions]

🎉 This PR is included in version 2.13.0 🎉

The release is available on GitHub release

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