fix(kanban): reset failure counters on unblock_task

When a task is manually unblocked (blocked → ready/todo), the
consecutive_failures counter and last_failure_error were left intact.
The next failure would immediately re-trip the circuit breaker because
the counter was still at or above the failure limit.

Reset both fields on unblock so the task gets a fresh retry budget.

Includes a regression test that verifies counters are zeroed.

hermes_cli/kanban_db.py

@@ -2718,7 +2718,8 @@ def unblock_task(conn: sqlite3.Connection, task_id: str) -> bool:
         ).fetchone()
         new_status = "todo" if undone_parents else "ready"
         cur = conn.execute(
-            "UPDATE tasks SET status = ?, current_run_id = NULL "
+            "UPDATE tasks SET status = ?, current_run_id = NULL, "
+            "consecutive_failures = 0, last_failure_error = NULL "
             "WHERE id = ? AND status = 'blocked'",
             (new_status, task_id),
         )