feat(errors): register the platform billing error codes

[yyyyaaa]

Summary

• The constructive-db billing rework (constructive-io/constructive-db#3904) raises new database error codes. This registers them, so errorEnvelope and the gateway return their proper HTTP status instead of treating them as unknown.
• The registry is regenerated with scripts/audit-db-errors.py. The public entries are curated in src/registry.ts.

Codes

Code	Class	Status	Context	Raised by
BILLING_SUBSCRIPTION_ACTIVE	public	409	{ entity_id, external_subscription_id }	the generated BEFORE DELETE guard: deleting an org or user that still has a live subscription
BILLING_QUOTA_EXCEEDED	public	429	none	the LimitTrackUsage gate trigger, when a row would pass the usage allowance (already on db main, previously unregistered)
BILLING_CHECKOUT_BINDING_INVALID	internal	500	{ entity_id, operation_id }	bind_checkout_session, a system-only seam, called with a null id (a caller bug)
BOOTSTRAP_OWNER_NOT_ACTIVE, SCHEDULED_JOB_NOT_ENQUEUED	internal	500	as raised	db main, newer than the last snapshot

FREE_PLAN_REQUIRED is dropped, because the rework no longer raises it.

// a P0001 with DETAIL {"code":"BILLING_SUBSCRIPTION_ACTIVE","class":"public",...}
httpStatusFor(parse(err)); // 409

Merge order

Merge after constructive-io/constructive-db#3904. Before merging, re-run scripts/audit-db-errors.py against the merged db main: this snapshot was taken from the db branch, so newer db-main codes may be missing.

🤖 Generated with Claude Code

https://claude.ai/code/session_01BqoF2inmLL6xPNjX1JiqXx

[tenki-reviewer]

Review complete. No issues found — approved ✅.

---

This PR extends the shared error registry with two billing-related codes: BILLING_QUOTA_EXCEEDED mapped to HTTP 429 and BILLING_SUBSCRIPTION_ACTIVE mapped to HTTP 409 with optional entity/external-subscription context, alongside a new test suite asserting their inventory presence and HTTP mappings. A review pass — including a sweep that initially suspected a missing BILLING_CHECKOUT_BINDING_INVALID definition — confirmed the generated registry already provides that code, so all assertions hold. No defects were found.

Files	Change
packages/errors/src/registry.ts	Adds curated defineError entries for the two new billing codes.
packages/errors/__tests__/billing-refusals.test.ts	New tests covering raised-code parsing, inventory alignment, and HTTP status mapping.
packages/errors/scripts/db-error-inventory.json	Regenerated inventory reflecting the new codes.

_{Reviewed commit: fc65ee6}