Easier cherry-picking: context menu, command palette, and file/hunk-level from a commit diff

[skoonin]

Summary

Make cherry-picking easier and more granular.

Desired behavior

• Right-click a commit (or multiple selected commits) -> "Cherry-pick selected".
• A command-palette action "Cherry-pick selected" for the current commit selection.
• When viewing another commit's diff, allow cherry-picking individual files or hunks into the working tree (partial cherry-pick), not just whole commits.

Scope / open questions

• Context-menu and command-palette entry points for whole-commit cherry-pick.
• File- and hunk-level apply from a historical commit's diff view.

Follow-up PR targets develop.