Dashboard hygiene: bulk-PATCH 10 longstanding May-vintage blocked tasks to cancelled (de facto retired by June 10 close-with-summary)

Long-tail dashboard-honesty cleanup. Ten fleet-tasks remain in status=blocked with updated_at=2026-05-29T04:40Z-vintage despite their underlying PRs being closed since June 10 close-with-summary execution (task 186bc3eb): 002e3c97 (alert wrapTransaction), d18e5573 (PR #10508 shepherd), 3116b189 (PR #10499), 923743f4 (PR #10498), 0e5f88e9 (PR #10401), 0d6039b2 (identity DeepSource registration), f24f2035 (PR #9353 coverage gate), a8ef2296 (PR #9886), d2d63920 (PR #9932), 591b8a38 (identity docker investigation). At lease time: (1) refresh GH_TOKEN via isolated-statement token-refresh; (2) for each task with a pr_number, run gh pr view <PR> --json state,mergedAt,closedAt; (3) if PR is CLOSED or MERGED, PATCH task to cancelled with result.summary citing the June 10 close-with-summary lineage (task 186bc3eb) or merge commit if applicable; (4) if PR is unexpectedly OPEN (defensive check), surface as a progress event on this cleanup task and skip the per-task PATCH; (5) for tasks without a pr_number (002e3c97, 0d6039b2, 591b8a38), PATCH to cancelled with result.summary noting they are superseded by the June 10 close-with-summary cohort retirement or by the agent-infra #319 / DeepSource activation arc; (6) PATCH this task to completed with result.cleaned[] (list of task IDs PATCHed) and result.skipped[] (list with reasons).