aprender: stop tracking roadmap.yaml + Pmat-Ticket trailers — the precondition for sovereign-ci roadmap-fragment-parity (A2 of #3676) #3709

Found while preparing #3676's coverage_on fix (cop ruling 2026-09-21 ~15:00Z; this issue is the (A2) row, linked to #3650).

paiml/.github's sovereign-ci.yml gained roadmap-fragment-parity in f02067e98 (paiml/.github#73). On pull_request, it fails the job when a PR's diff touches docs/roadmaps/roadmap.yaml ("GENERATED — run 'make roadmap-aggregate' on the default branch, never edit it in a PR"), or when a docs/roadmaps/entries/*.yaml in the diff has no Pmat-Ticket: <id> commit trailer on the branch. Its header assumes that a repo with entries/ has stopped committing the aggregate.

aprender has entries/ but still commits the aggregate, deliberately:

• every row commits the aggregated roadmap.yaml;
• make roadmap-aggregate-check requires it in sync;
• scripts/batch_fold.sh --regen regenerates it in every batch;
• none of main's recent commits carries a Pmat-Ticket: trailer.

So bumping aprender's pin of sovereign-ci.yml past f02067e98 (needed for coverage_on: tag, #3676) would have turned every aprender PR red. The interim fix is (A1) in paiml/.github: the step activates only when roadmap.yaml is NOT tracked. That keeps it off for aprender until this row flips it on.

This row is the migration, #3650's own direction: committed generated files are the merge-conflict source, measured at 16–32% of PR-CI runner time.

done_when

• aprender stops tracking docs/roadmaps/roadmap.yaml. It is produced from entries/ (make roadmap-aggregate) where it is consumed: on main after merge, and on demand locally. roadmap-aggregate-check moves from "the committed file is in sync" to "the aggregate generates cleanly and idempotently from entries/".
• scripts/batch_fold.sh --regen no longer regenerates roadmap.yaml (the other generated files are The committed roadmap.yaml AGGREGATE re-creates the conflict the fragments removed — every fragment-minting PR regenerates it, adjacent ids conflict in the merge-queue group build (#3637 UNMERGEABLE behind #3631; 18 such PRs armed tonight) #3650's scope).
• Every commit that adds or edits a fragment carries Pmat-Ticket: <id>, enforced locally so it isn't discovered in CI.
• With roadmap.yaml untracked, sovereign-ci's roadmap-fragment-parity switches ON by itself (the (A1) key). A PR that re-adds the aggregate, or a fragment without its trailer, goes red, proven on a real PR.

Refs #3650 #3676 #3688