feat(logger): set diagnose=False to prevent exposing secrets in Loguru traceback logs

[aoright]

Pull Request Checklist

• Target branch: The pull request targets the dev branch.
• Description: A concise description of the changes is provided below.
• Changelog: A changelog entry following Keep a Changelog format is included at the bottom.
• Testing: Manual tests have been performed to verify the fix works.
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Changelog Entry

Description

Loguru traceback logs evaluate and print local variable values (by default diagnose=True), which can easily leak sensitive information (such as API keys, Bearer tokens, DB connections, or passwords) into standard stdout/JSON logs when exceptions occur in production environments.

This PR sets diagnose=False on the configured Loguru stdout, JSON, and audit log file sinks, preventing local variable evaluation while retaining the clean formatted traceback.

Fixed

• Set diagnose=False on stdout, JSON, and audit log file sinks in logger.py.

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[sanmaxdev]

Looks good. Loguru enables diagnose by default, and this patch disables it on all three start_logger sinks: JSON/stdout plus audit file output.

Checked the diff against backend/open_webui/utils/logger.py and confirmed it applies cleanly.