fix(cad): surface Zoo error detail in CAD generation rejections

[devin-ai-integration]

Summary

text_to_cad multi-part generations report every failing part as:

<part>: The CAD generation service rejected the request.

The Zoo WebSocket error frame actually carries detail (and sometimes error_code / request_id), but errorDetail() in packages/cad/src/zookeeper.ts was collapsing it to the generic string regardless of the payload.

Changes

• errorDetail() now extracts error string / detail / message and includes code= / request_id= metadata.
• Falls back to a bounded JSON dump for unknown error shapes instead of swallowing them.
• Exports errorDetail() and adds unit tests for string errors, object details, code/request_id metadata, long-value truncation, and the fallback generic message.

This makes enclosure_shell, rear_cover, kickstand, etc. failures actionable instead of opaque — the next rejection will show the actual Zoo reason (e.g. quota, unsupported geometry, bad request).

Link to Devin session: https://app.devin.ai/sessions/d846e91524fc43aca04de9649aeb2300
Requested by: @alanshen27

[devin-ai-integration]

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