fix: clear empty statistics status bar content

[vycdev2]

Summary

• clear the statistics status bar text and tooltip when their configured templates render empty instead of retaining stale content
• add regression coverage for changing both values from non-empty to empty
• document the user-visible fix in the 5.3.0 changelog

Verification

• npm test — passed: 135 tests
• npm run compile — passed: webpack development build completed
• npm run format:check — passed: all matched files use Prettier formatting
• git diff --check upstream/develop...HEAD — passed

Risk

• Low: the change only removes empty-value early returns, allowing the existing status bar property setter to clear prior content.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.