refactor: separate runtime and administration clients

[ralphhanna]

Summary

Separates pure workflow-execution requests from workflow-definition administration.

• Keeps execution calls on the runtime client
• Introduces explicit administration clients
• Removes model-management methods from the runtime client contract
• Documents the change in CHANGELOG.md

Stack

This is client #2 and the base for the canonical v1 client PR.

Validation

• Client boundary tests pass.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reject missing administration responses

When a request encounters a network error or any non-2xx response, WebService.invoke catches the Axios exception and resolves with undefined; this optional chain therefore treats the failed administration call as successful and lets list, delete, rename, or load resolve with undefined despite their declared return types. Make a missing result an error in this helper and in the identical BPMNAdminClient2 helper so callers can reliably detect failed administrative operations.

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