fix: show repository paths in repository picker

[aidxun]

What changed

• added repository rootPath to the workspace-start repository options returned from the backend
• extracted a shared repository menu component and show the selected or hovered repository directory under the picker list
• added the matching changeset note

Why it changed

Showing only repository names makes it hard to distinguish similarly named repositories when creating a workspace. Displaying the directory path in the picker makes selection unambiguous without expanding the main layout.

Follow-up / test notes

• Fixes Feature request: Add custom repository display names #472
• Verified with bun run typecheck
• No targeted UI test coverage was added in this change

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