fix(canvas): address PR board review feedback

Fence review results with required queue tokens, lock concurrent GitHub actions, recover persistence after errors, and reopen feedbacked PRs on new commits. Guard detail request races and add modal focus management and keyboard tabs with regression coverage.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8045e7e0-dfd7-425a-9131-21ea5ca1553e

.github/extensions/open-pr-board/lib/github.mjs

@@ -147,6 +147,7 @@ function normalizePullRequest(raw) {
         isDraft: Boolean(raw.isDraft),
         baseRefName: raw.baseRefName,
         headRefName: raw.headRefName,
+        headRefOid: raw.headRefOid,
         additions: raw.additions ?? 0,
         deletions: raw.deletions ?? 0,
         changedFiles: raw.changedFiles ?? 0,
@@ -175,6 +176,7 @@ const LIST_FIELDS = [
     "labels",
     "baseRefName",
     "headRefName",
+    "headRefOid",
     "additions",
     "deletions",
     "changedFiles",