feat(api): installable accounted-api agent skill + openapi-to-skill generator (#1516)

* feat(api): installable accounted-api agent skill + openapi-to-skill generator

Three layers, per the July/August 2026 agent-skills ecosystem (skills.sh /
npx skills add, as used by Stripe/Cloudflare/Supabase for their APIs):

- skills/openapi-to-skill/: generic, installable skill that turns any
  OpenAPI spec into a consumer-side integration skill, with a portable
  stdlib-only inventory/condenser tool and an output template + quality
  checklist encoding the distill-not-restate methodology.
- skills/accounted-api/: the installable skill for our own API, rendered
  deterministically by scripts/api-skill/generate.ts from the v1 endpoint
  registry + hand-authored overlays (auth, conventions, domain gotchas).
  CI gate: npm run apiskill:check (core-build.yml).
- lib/api/v1/registry.ts: generateOpenApiSpec now emits requestBody (incl.
  multipart binary parts) and path parameters, and the Zod converter learned
  .default()/z.record()/.pipe()/.transform(), so the public spec carries
  request contracts instead of prose-only.

Docs: /docs/api landing + /llms.txt now point agents at the skill install;
corrected the stale test-key description in the landing (test keys read
real data and force dry-run writes; they are not sandbox-company bound).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(skills): escape backslashes in markdown table cells (CodeQL js/incomplete-sanitization)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/core-build.yml

@@ -44,6 +44,13 @@ jobs:
         # so drift here means filings tagged against a stale concept set.
         run: npm run taxonomy:check
 
+      - name: Verify the accounted-api agent skill is in sync with the registry
+        # Fails if a v1 endpoint / registry schema / overlay changed without
+        # regenerating skills/accounted-api (npm run apiskill:generate). The
+        # skill is the installable API reference for external coding agents;
+        # drift here means agents integrate against stale endpoint contracts.
+        run: npm run apiskill:check
+
       - name: Lint ratchet (no new ESLint errors)
         # `npm run lint` was never wired into CI, so ~60 legacy errors
         # accumulated. This ratchet (sibling of check:guards) fails only when