File a quota-increase request

Files a pending request to raise one quota dimension of the scope's subscription to requestedLimit, for review by a platform operator. The current EFFECTIVE limit (configured default overlaid with any operator override) is resolved server-side and recorded as currentLimit. The record is returned 201; an approval later applies the granted limit to the subscription. Validation: quotaId must be a known quota id (e.g. q-vcpus) → else 404 NOT_FOUND; requestedLimit must be an integer in 0..2147483647 and strictly greater than the current effective limit (field requestedLimit); justification at most 1000 characters; unknown properties are refused — every violation → 422 VALIDATION_FAILED. RBAC: MANAGE on billing plus the billing:write token scope (a reader cannot file). A tenant on non-payment hold is read-only → 403. Async & state: Synchronous — 201 with the persisted QuotaIncreaseRequest in status pending. Errors: 401 unauthenticated; 403 caller lacks billing MANAGE / token scope, or tenant on hold; 404 unknown scopeId or quotaId; 409 CONFLICT a request for the same quota is already pending for this subscription (details.reason QUOTA_REQUEST_PENDING, details.requestId); 422 invalid body; 500 internal failure. Idempotency/Concurrency: No Idempotency-Key. At most one pending request per (subscription, quota id): concurrent filings are serialised and the loser gets the 409.