Replace turn chips with dropdown and add conflict file submenu

[BunsDev]

Summary

• Replaced the DiffPanel turn chip strip with a compact dropdown selector for switching between changes.
• Simplified the header by removing horizontal scroll handling and chip-specific navigation logic.
• Expanded the Git actions conflict UI to show a submenu of conflicted files, with per-file editor opening and an Open all action for multi-file conflicts.

Testing

• Not run
• No automated checks were executed for this branch in this pass