fix: disable empty reasoning expansion

[easyops-eve]

Summary

Elevo Messenger now treats vip.elevo.reasoning.empty: true as an explicit empty reasoning marker. For these fallback reasoning messages, the UI shows only the duration summary and does not offer the expand interaction.

Implementation Plan

• Add a small reasoning metadata helper that preserves legacy empty-body behavior.
• Extend Matrix reasoning metadata parsing with empty?: boolean.
• Use the helper in MsgTypeRenderers so explicit empty fallback messages are non-interactive even when the Matrix body contains Thought for N seconds.
• Add focused tests for explicit empty metadata, legacy non-empty reasoning, and legacy empty-body reasoning.

Verification

• npm test -- src/app/components/message/MsgTypeRenderers.test.ts --run
• npm test -- --run
• npm run build
• git diff --check

npm run typecheck is still blocked by existing default-branch issues unrelated to this change: html-dom-parser package export typings and existing TUploadContent / Blob.name errors.

[github-actions]

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