feat: Add Payload CMS connector (API Key + GraphQL)

[major-connector-creator]

Payload CMS Connector — npm package changes

Adds TypeScript client, schemas, and payload builders for the Payload CMS connector.

New Files

• src/schemas/api-payloadcms.ts — ApiPayloadCMSPayload interface (type/subtype/query/variables/operationName/timeoutMs)
• src/clients/payloadcms.ts — PayloadCMSResourceClient with query() and mutate() methods
• src/payload-builders/payloadcms.ts — buildPayloadCMSQueryPayload and buildPayloadCMSMutatePayload functions

Modified Files

• src/schemas/index.ts — Export ApiPayloadCMSPayload, add to ResourceInvokePayload union
• src/schemas/response.ts — Add PayloadCMSInvokeResponse type alias
• src/index.ts — Export PayloadCMSResourceClient and PayloadCMSInvokeResponse
• src/payload-builders/index.ts — Export payload builders
• src/payload-builders/from-extracted-params.ts — Add payloadcms routing case for query/mutate
• bin/generate-clients.mjs — Add payloadcms → PayloadCMSResourceClient mapping, add to valid types and help text

Why a dedicated subtype?

Payload CMS uses a unique Authorization header format: {collectionSlug} API-Key {apiKey}. A dedicated connector auto-constructs this header, giving a cleaner UX than the generic GraphQL connector.