fix(views): align revision-conflict actions with their previews (#7634)

The concurrent-edit conflict block rendered both actions in one row under
the left edge of the box, so "keep my version" sat under the SERVER
preview it discards and "use the latest version" sat next to it — the
spatial pairing was inverted (#7624).

Replace the single freeform `actions` slot with `serverAction` /
`localAction` and render them in the same two-column grid as the labels
and the diff, one action per column. The diff never stacks, so the
pairing holds at every window width; button left edges line up with
their column headers. Both buttons are now `outline` — they are peer
choices under equal-weight panes, and the discard-my-edits side should
not read as the quieter one.

Labels are unchanged: under their own column, "使用最新版本" / "保留我的
版本" are already unambiguous.

Co-authored-by: J <bohan@devv.ai>
Co-authored-by: multica-agent <github@multica.ai>