[Feature Request] Add merge strategy option for single-branch merge

[nelson870708]

Description:
Currently, when merging multiple branches, the merge dialog provides an option to choose merge strategies (e.g., --strategy=ours).
However, when merging a single branch, the UI performs the merge immediately without offering any strategy selection.

This inconsistency makes it impossible to use alternative merge strategies (such as ours) for simple one-to-one merges.

Expected behavior:
When merging a single branch, show the same merge strategy selection UI (or at least allow specifying a default strategy).

Motivation:
Sometimes we need to merge a single branch while always keeping the current branch's content (--strategy=ours), but currently there’s no way to do that in the single-branch merge flow.

Additional context:
I reviewed the code and noticed that the multi-branch merge path already supports strategy options.
I’d be happy to help implement or test this if it aligns with the project goals.