feat(unkey): add the Unkey SDK

[Mkassabov]

Caution

STOP — there is already an open distilled PR for Unkey by someone else. Distilled's generator pipeline has changed a lot; this is a new implementation, not a rebase of theirs. Review both and do not merge this and theirs blindly.

• @Vicentesan — feat: add unkey support #323

This is the requested Unkey SDK. distilled#323 is an existing Unkey SDK PR (not an issue); this PR is a new generator-pipeline implementation of the same request.

Adds @distilled.cloud/unkey, generated from a first-party API description.

• Related PR: feat: add unkey support #323
• Fetch script: stacks/distilled-submodules/spec-repos/unkey/fetch-specs.ts
• Spec source: first-party OpenAPI in unkeyed/unkey (svc/api/openapi/openapi-generated.yaml)
• Convert/generate: packages/unkey/scripts/{convert,generate}.ts
• Mirror repo distilled-mirror/spec-mirror-unkey is created by the distilled-submodules stack on merge to main. Until then, regenerate with pnpm specs:local unkey and DISTILLED_SPECS_LOCAL=1 pnpm generate unkey.

pnpm specs:link unkey recorded the .gitmodules stanza (shallow = true).