Harden task title rendering for emoji

[nguyenduc071912]

Summary

Hardens task-title rendering for complex emoji titles such as ZWJ family sequences.

• Renders task titles with an explicit text node instead of reassigning text content during each render
• Keeps complex titles out of dynamic aria-label strings on action buttons
• Adds a regression test confirming sanitizeTasks preserves the family emoji sequence from the issue

fixes #10

Tests

npm test
npm run lint

[codebounty-dev-bot]

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