git_graph: Improve ref chips

[nguyenphutrong]

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

This PR improves the way Git refs are rendered in Git Graph rows and commit details by giving ref chips clearer visual treatment.

The ref chip updates include:

• Dedicated stash and tag icons
• Leading-icon and label-weight support in the shared Chip component
• Distinct chip icons for branch, tag, stash, and checked-out branch refs
• A clearer checked-out branch chip using stronger visual emphasis
• Stash labels rendered as stash@{n} when the stash commit can be matched to cached stash entries, instead of showing the raw refs/stash decoration
• A fallback to the original ref name when the stash cache does not contain the matching commit

This keeps the raw Git decoration data intact and only adjusts the display name used by Git Graph when rendering stash refs.

Testing performed:

• cargo fmt --all
• git diff --check
• ./script/clippy -p git_graph --tests

Release Notes:

• Improved Git Graph ref chips for branches, tags, and stashes.

[SomeoneToIgnore]

Autoclosing all draft PRs with no activity for 2 weeks or over, this one also has conflicts: