feat(knowledge): regenerate _schema.md on the doc-integrity pass (generator is currently dead code)

[elhoim]

GenerateKnowledgeSchemaDoc.ts is dead code — nothing in the tree invokes it. Two consequences follow:

1. _schema.md does not exist on a fresh install. The schema doc the archive is supposed to be governed by simply isn't there.
2. Where it does exist, it drifts from KnowledgeSchema.ts, which the doc itself names as the single source of truth.

This is not theoretical

On the archive this was found on, _schema.md declared kb-v3 canonical while describing 0.9% of the notes it governed — 17 of 1,801. The gap went unnoticed for as long as it did precisely because nothing regenerated the doc, so there was no moment at which the declaration and the reality were compared.

The same class of drift bit again during the repair: a change to the validation rule in validate() would not have appeared in the generated doc, because the generator reads the PER_TYPE_REQUIRED data table. Caught only because the doc was regenerated by hand and read.

The change

Wire the generator into DocIntegrity, which already runs a cross-reference pass, so _schema.md is rebuilt from KnowledgeSchema.ts every time integrity is checked.

• Fire-and-forget, non-fatal. A generator failure logs and does not break the doc-integrity pass.
• Subprocess, not import. GenerateKnowledgeSchemaDoc.ts executes main() at import time, so importing it would run the generator as a side effect of loading the handler.

Net effect: the schema doc exists on every install, and cannot silently disagree with the code that defines it.

Companion to #1684, which fixes a rule in the same schema. That PR changes behaviour in validate(); this one guarantees the generated doc reflects such changes.

[danielmiessler]

Ported into source with credit — thank you.

The public repo is generated from a private tree at release time, so merging here would be reverted at the next cut; the intent landed in source instead, with your handle and this PR number in the code comment at the fix site.

One note: local source had moved since your base, so the port is adapted rather than byte-identical — same fix, fitted to current code. Details are in the commit. Closing as ported.