fix(api): give the shared write ceiling a code a client can branch on

The eleven single-record writes answered their shared 429 with prose and
nothing else, while the envelope's own description tells a client to
branch on `meta.errorCode`. On `POST /api/medications/[id]/intake` and
`POST /api/cycle/day-logs` a second, narrower bucket can answer 429 as
well, so the presence of the rate-limit headers was the only thing
telling the two refusals apart.

All eleven now carry `record_write.rate_limited`, the catalogue lists
it, the published 429 names it, and the contract test fails if a site
stops emitting it or the sentence stops publishing it.

The same description now states what a client could not predict from
"300 requests per 60 seconds": refused requests count too, because the
check runs before the body is read.

src/lib/openapi/error-codes.ts

@@ -251,6 +251,7 @@ export const ERROR_CODE_CATALOGUE: Readonly<Record<string, readonly string[]>> =
       "profile.update.invalidBody",
       "profile.update.nothingSaved",
     ],
+    record_write: ["record_write.rate_limited"],
     "report-selection": [
       "report-selection.body.invalid_json",
       "report-selection.body.invalid_shape",