v0.17.4 — generate-docs: standalone mode rule, findings writer, single-source stable keys

A session-wide review of the v0.16.2–v0.17.3 work surfaced three soft spots, all in /architect:generate-docs. None change behaviour that was already exercised — they pin down what was previously derivable but implicit.

Fixed

Standalone mode determination is now stated. Invoked with no --issue and not as a step of another skill, the resolved root decides the mode: a root under generated/ is scaffold, anything else is delivery — with --issue required before any tracker write, and, when the run has no Issue to reference, commits still landing on the working branch and drift findings going to the user only.

The findings section has a stated writer and timing. It is produced by Step 5 verification but was listed only in Step 4's section table, leaving a first run with no stated writer. Step 5 now writes it after verification in scaffold mode; the Step 4 listing covers re-runs, where prior findings already exist to carry.

The stable key list has one source of truth. It lived in both SKILL.md prose and the contract test's STABLE set, with only a comment as sync guard. marker-mechanics.test.py now parses the list from SKILL.md's "Section keys are stable (…)" sentence — failing hard if the sentence disappears, with a fallback list so the mechanics checks still run if the file is copied elsewhere. Verified: all 8 keys parse, both fixtures pass, the fallback path passes.

Full changelog: CHANGELOG.md · CHANGELOG_ja.md