Story: Clear the stale block on the literate template task

Return the literate-template task to the backlog, so a workstream that can proceed is not held by a dependency that finished three months ago.

• The task is no longer BLOCKED.
• Its blocked_on and blocked_since are cleared.
• The story's task row and the task file agree.
• What blocked it is recorded, so the reason it was paused is not lost.

• The task is unblocked, not closed. Its blocker is DONE, but the work is not: the acceptance asks for every template org to be split, and only the cpp_repository pilot landed. Returning it to BACKLOG is what the block clearing means; closing it would have been the false "done" this pass has been careful to avoid.
• The audit will still list it. Its rule is "open task whose pull requests have all merged", and #1743 merged the pilot. That is a true statement about a partly-done task rather than a stale block, so the finding stays and means something different now.

• Doing the split. This story clears the block; the work belongs to the codegen workstream.

Done. The task is BACKLOG, its blocked_on and blocked_since are empty, its story row agrees, and its Next names the dependency as the state it is in rather than the state it waits for.