fix(spec): correct stale tags note in doc.json liveness ledger

[os-steve]

Fixes#9310

What was stale

packages/spec/liveness/doc.json's _note claimed DocSchema declares no
tags key, so authoring tags: on a doc was a parse error, every doc
reached the resolver with tags === undefined, and a book group's
include: { tag: '<t>' } rule could therefore never match.

That was true when the note was written, but doc.zod.ts:126 has declared
tags: z.array(z.string()).optional() since 17.0.0 (#4509, ADR-0049) — the
enforce half of enforce-or-remove for this key, with the fix's own history
in the comment block immediately above the declaration (L111–L122). The
ledger's own props.tags entry already reflects status: "live" with that
full history; only the top-level _note paragraph had gone stale.

What changed

Corrected the note's last sentence to a current-state statement rather than
deleting it outright: it still carries load-bearing cross-references (the
book-side include: { tag } rule, the REST corpus offset at
rest-server.ts:2965) that are useful context for a reader of the ledger,
so it now says tags was declared and the { tag } variant went live, and
points at the props.tags entry below for the full history instead of
repeating it. No behaviour change, no verdict changes, no other rows
touched.

Local gates (HEAD 1543ad904)

Derived via node scripts/pm/dispatch-gates.mjs packages/spec/liveness/doc.json:

• pnpm --filter @objectstack/spec run check:empty-state — pass
• pnpm --filter @objectstack/spec run check:liveness — pass
• pnpm --filter @objectstack/spec run check:strictness-ledger — pass
• pnpm --filter @objectstack/spec run check:variant-docs — pass
• node scripts/check-nul-bytes.mjs packages/spec/liveness/doc.json — pass

Not run: pnpm --filter @objectstack/spec test — no test suite reads
liveness/doc.json's _note (checked via grep across packages/spec/**/*.test.*).

Out-of-scope findings (same stale claim restated elsewhere)

The file surface for this card is packages/spec/liveness/doc.json only.
Grepping sibling liveness files for the same assertion found it restated in
two more places, both outside this diff — filed as #9316:

• packages/spec/liveness/book.json:77 (props.include.note)
• packages/spec/liveness/README.md:808 (the book row)

Generated by Claude Code

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Generated by Claude Code

[github-actions]

📓 Docs Drift Check

Nothing in this diff resolved to a documentable surface (no symbol, route or SDK anchor derived from 1 changed package(s)), so this run has no opinion about the docs.

What this run could not see

• 1 changed file(s) yielded no anchor (packages/spec/liveness/doc.json) — pages documenting those are invisible to this run

Coarse fallback — 113 page(s) merely mention a changed package (the pre-#9192 predicate, kept for the deliberately-wide backstop): node scripts/docs-audit/affected-docs.mjs --json origin/main → packageMentionDocs.