records/modify: add zoneID, desiredKeys, numbersAsStrings request options

[leogdion]

Background

Follow-up to #14 (Modifying Records — CLOSED). A gap review of openapi.yaml against the Web Services reference (webservices.md:1437-1443) found the records/modify request body is missing several documented top-level options.

Current state

records/modify request body (openapi.yaml:114-123) exposes only operations and atomic.

What needs to be done

Add to the request body schema:

• zoneID — target zone for the operations.
• desiredKeys (array of field names) — limit the fields returned in the modify response.
• numbersAsStrings (boolean) — return numeric field values as strings.

Implementation notes

• Edit openapi.yaml only, then regenerate via ./Scripts/generate-openapi.sh. Never hand-edit Sources/MistKitOpenAPI/.
• Surface the new options through CloudKitService modify/create/update methods as appropriate.
• Record-sharing creation keys (createShortGUID, forRecord, publicPermission, participants) are also a modify-request gap but are tracked separately under Accepting Share Records (records/accept) #42.