MoveIssuesOnProjectColumn updated `project_issue` with a WHERE clause on
issue_id only. An issue assigned to several projects has one project_issue
row per project, so moving it within one project rewrote project_board_id
for every project the issue belonged to, detaching it from all the others.
Scope the UPDATE to (issue_id, project_id) so only the target project's
row changes. Mirrors the fix already present in upstream/main.
Adds an integration regression test asserting an issue in two user
projects keeps its column in the other project after a move. Fixes#17.
Claude
078459c497