fix: allow array content in isValidMessage for multimodal support

[shenald-dev]

This PR fixes a correctness bug in isValidMessage where msg.content was strictly required to be a string. For modern OpenAI multimodal compatibility, the content field can be an array of objects (e.g. text and image URLs). This change allows arrays via Array.isArray, preventing valid multimodal requests from being rejected. It also includes an updated test suite and documentation in .jules/bolt.md.

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PR created automatically by Jules for task 7123164898808196545 started by @shenald-dev

[google-labs-jules]

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[shenald-dev]

Looks good, merging this in. CI is green and everything checks out 👍

Allow msg.content to be an array for multimodal OpenAI support.

[google-labs-jules]

Looks good, merging this in. CI is green and everything checks out 👍

Allow msg.content to be an array for multimodal OpenAI support.

Acknowledged.