chore(changeset): patch @objectstack/spec — the refusal string ships

Measured, not assumed: `packages/spec/package.json` `files[]` publishes both
`dist` and `src/**/*.zod.ts`, and after a build the new citation appears in
four published bundles (`dist/index.js`, `dist/index.mjs`,
`dist/browser/index.js`, `dist/browser/index.mjs`) with the old spelling at
zero. Published bytes move, so `skip-changeset` does not apply.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012GKcPZbMoGq7WPzKLfRBTU

Author: claude

.changeset/one-app-rule-adr-0019-citation.md

@@ -0,0 +1,17 @@
+---
+"@objectstack/spec": patch
+---
+
+fix(spec): the one-app-per-package refusal cites the record it means, `ADR-0019 (app-as-consumer-unit) D3`
+
+`ADR-0019` names **two** records in this repository — `0019-app-as-consumer-unit` (D3 = a `type: 'app'` package defines at most one app) and `0019-approval-as-flow-node` (D3 = deprecating `ApprovalProcessSchema`). Both have a D3, and `stack.zod.ts` cited the bare number for both, so an author following the refusal's own citation was as likely to reach the wrong decision record as the right one.
+
+The three citations of the app-cap rule now name the record:
+
+- the `STACK_SINGLE_APP_VIOLATION` message — the only one an app author ever sees;
+- the `validateSingleApp` docblock;
+- the `StackSingleAppViolationError` docblock.
+
+Only the message tail changed: `An 'app' package must define at most one app, but found N (…)` is untouched, so any consumer matching on that prefix is unaffected. The rule, the refusal's condition and `defineStack`'s behaviour are unchanged.
+
+The approvals-side citations are deliberately left bare — repo-wide ADR-number disambiguation is tracked separately.