Resolve conflicts block by block in the terminal #1408

The pull screen has p (crew proposes). Add a resolve screen: per block ours/theirs/both, then Finish through resolveConflicts. Follow-up to #1351.

The conflict-resolution code from #1351 (resolveConflicts, the editor, the markers parser) isn't in main or in this branch. Pull #1351 is still open and unmerged, so the screen this issue asks for has nothing to call.

DECLINED: This issue depends on #1351, which is still an open pull and hasn't landed on main. resolveConflicts (src/actions/conflicts.ts) and the conflict-block parser (src/git/markers.ts) don't exist in this branch, and neither does the p (crew proposes) key on the pull screen. Writing a resolve screen would mean inventing both the action and the block model from #1351's description, and they would very likely clash with the real ones when it merges. Once #1351 is merged, re-assign this issue and I'll build the screen on top of it. It would be a new src/tui/screens/resolve.ts opened from the pull screen when the pull is conflicted, with per-block ours/theirs/both keys and a Finish key that calls resolveConflicts.

Parked by the crew: the run ended without a pull: no changes pushed: The conflict-resolution code from #1351 (resolveConflicts, the editor, the markers parser) isn't in main or in this branch. Pull #1351 is still open and unmerged, so the screen this issue asks for

Parked by the crew: the run ended without a pull: declined: Nothing has changed since my last report. #1351 is still open and unmerged, so resolveConflicts (src/actions/conflicts.ts) and the conflict-block parser (src/git/markers.ts) are not on main.

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the run ended without a pull: no changes pushed: The conflict-resolution code from #1351 (resolveConflicts, the editor, the markers parser) isn't in main or in this branch. Pull #1351 is still open and unmerged, so the screen this issue asks for
2. the run ended without a pull: declined: Nothing has changed since my last report. #1351 is still open and unmerged, so resolveConflicts (src/actions/conflicts.ts) and the conflict-block parser (src/git/markers.ts) are not on main

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Deferred by the planner. The resolve screen needs resolveConflicts and the conflict-block parser from pull #1351, which is open and unmerged. It sits behind the Later gate (#595) until #1351 lands. Then the owner can open it.