Task: Scaffold story: Hotfix: Site build needs live GNU ELPA

Scaffold the hotfix story and its tasks, wire them into sprint 27, and raise the PR that carries the fix.

• The story, scaffold task and implement task exist and are wired into sprint 27.
• PR #2693 carries the fix.

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

Every number this task claims about a tree, with the command that produced it and the commit it was measured at. A number without both is not a measurement, because a clean-up record describes a tree and trunk moves under a branch: a consumer count, a gate's component count and a suite's size all change with no code changing, and the reader of a bare number cannot tell which tree it came from. Where the raw output matters, put it in an evidence/ file beside the task and name that file in the Command column.

Manual QA scenarios (scaffolded via compass add test_scenario) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.

The story and its two tasks exist and sprint 27 carries the story. PR #2693 carries the fix on hotfix/site-build-needs-live-gnu-elpa.