feat(tui): use ellipsis in middle of file path instead of truncating for modified files list

[angristan]

Closes #9592

What does this PR do?

I watched this video a couple of days ago where Scott Jenson talks about early on macOS where they moved the ellipsis in the middle of the file instead of the end to not trim critical information.

I found myself needing this in opencode, because when paths get long, the actual filename get truncated so the modified files list is less useful.

How did you verify your code works?

After/before:

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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

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No duplicate PRs found

[Copilot]

Pull request overview

This PR improves the user experience in the TUI by displaying file paths with middle truncation (ellipsis in the middle) instead of end truncation in the modified files list. This preserves the filename and extension, which are often the most important parts of the path.

Changes:

• Added constants for sidebar width calculations to enable dynamic file path truncation
• Updated modified files list to use Locale.truncateMiddle() with calculated width based on available space
• Width calculation accounts for sidebar padding and stats display (additions/deletions)

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[angristan]

OK I fixed the two-spaces gap between filename and diff, now it's one:

[johanohly]

Hope it's OK to bump this, I'd really like this as well.

[github-actions]

Closing this pull request because it has had no updates for more than 60 days. If you plan to continue working on it, feel free to reopen or open a new PR.