feat(desktop): Fork Message from Message Nav

[dbpolito]

What does this PR do?

Adds button for forking session from message nav, only on hover

How did you verify your code works?

Desktop:

Mobile (different colors but similar constrast as it starts from a different gray):

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search results, I found one potentially related PR:

Related PR:

• PR Feature Request / Proposal: fork session from message via CLI + copy command message dialog #5172: "Feature Request / Proposal: fork session from message via CLI + copy command message dialog"
  • Feature Request / Proposal: fork session from message via CLI + copy command message dialog #5172
  • This addresses forking sessions from messages, which is related to the fork functionality in your PR, though it focuses on CLI and copy command rather than the desktop message nav button.

The other results (PRs #4709, #5873, #6962) appear to be about different features (token usage, IDE integration, and session backfill respectively) and are not duplicates.

Your PR #7845 appears to be addressing a specific desktop UI enhancement for forking from the message navigation, which seems to be a distinct new feature rather than a duplicate of existing open work.