Close task bookkeeping when raising the PR, not after review

Close a task's bookkeeping (state → DONE, story's Tasks row, and the * Result section) when raising its PR — as part of pr-raise, not as a separate step deferred until the review round finishes.

Why: The agile-close-task skill's original guidance ("close at end of review round, before merge, so bookkeeping rides the PR") meant a dedicated close-task commit landed after every review-round fix commit, adding its own push + CI cycle on top of the round's own. Closing at PR-raise time instead means review-round fixes are the only commits still needed after the PR opens — no trailing bookkeeping round-trip stacked on the end. Called out explicitly after this happened on PR #1446 (task closed only after two follow-up review rounds had already landed, each with its own push/CI wait).

How to apply: When running pr-raise for a task-backed branch, do the task's close-out (state, story row, Result) in the same commit sequence as opening the PR, before pushing. Review-round fixes after that still get their own commits/replies as normal — just no separate "close task" commit tacked on afterward. If the task's scope shifts mid-review (e.g. a review finding expands the work), it's fine to amend the Result section in a follow-up commit, but the DONE state itself should already be set from the PR-raise step.