tui 6/8: delete + empty-commit handling & branch dissolve

[freshtonic]

Parent

#1 — git queue tui — interactive queue/history editor (TUI)

What to build

Delete a commit, with the empty-commit and branch-dissolve rules.

• Delete the selected commit (rebase drops it; descendants replay, going through the conflict escape hatch if needed).
• Empty-commit handling (follow jj): an operation that leaves a commit empty and description-less auto-drops it; an empty commit that has a description is kept and rendered (empty). Explicit delete always removes, empty or not.
• Dissolve: deleting a branch's only commit empties the branch — prompt to dissolve it; if a dissolved branch has an open PR, warn (reuse edit's PR/remote-branch messaging).

Acceptance criteria

• Delete removes the selected commit and rebases descendants immediately.
• A commit left empty and description-less is auto-dropped; an empty commit with a description is kept and shown as (empty).
• Deleting a branch's last commit prompts to dissolve the branch.
• Dissolving a branch with an open PR prints a warning.
• Delete is undoable.
• Engine integration tests cover delete, auto-drop vs keep-empty, and the dissolve path.

Blocked by

• tui 4/8: reorder + conflict escape hatch (resolve/undo, suspend/resume) #5 (ticket 4 — reorder & conflict machinery).