fix(mqtt): propagate JSON query evaluation errors

[larsch]

Summary

• Propagate MQTT JSONata evaluation errors instead of silently discarding them.

• Report errors using the same format as HTTP(S) JSON-query monitors:

  Error evaluating JSON query: <error>. Response from server was: <message>
  

• Prevent invalid expressions such as $toMillis("junk") from producing an empty value that numeric conditions interpret as 0.

• Add a focused regression test covering an invalid $toMillis() expression with an MQTT json_value condition.

• Preserve the existing HTTP(S) regression test confirming that invalid $toMillis() input is propagated.

• Resolves MQTT JSON query conditions treat expression errors as zero #7642.

• Full disclosure; AI was used to troubleshoot, debug, and implement this test and change, but I have reviewed and to my ability, the change and test are sound. The change is a one-liner, which brings the behavior into consistency with HTTP(s) endpoints. The focused unit test pass, and I have tested on a live install and verified the effectiveness of the fix.

Please follow this checklist to avoid unnecessary back and forth (click to expand)

• ⚠️ If there are Breaking change (a fix or feature that alters existing functionality in a way that could cause issues) I have called them out
• 🧠 I have disclosed any use of LLMs/AI in this contribution and reviewed all generated content.
  I understand that I am responsible for and able to explain every line of code I submit.
• 🔍 Any UI changes adhere to visual style of this project.
• 🛠️ I have self-reviewed and self-tested my code to ensure it works as expected.
• 📝 I have commented my code, especially in hard-to-understand areas (e.g., using JSDoc for methods).
• 🤖 I added or updated automated tests where appropriate.
• 📄 Documentation updates are included (if applicable).
• 🧰 Dependency updates are listed and explained.
• ⚠️ CI passes and is green. PENDING.

[github-actions]

Thanks for the PR! If anyone would like to help with testing, run: npx kuma-pr larsch:fix/mqtt-json-query-error (requires Node.js and Docker)

[github-actions]

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