fix: Export button pulse

[gravypizza]

Description

• Added a pulse animation to the Export button when a file is loaded and the editor is ready to export (status === "idle").
• The animation stops automatically during export and after export completion.
• Uses motion-safe:animate-pulse to respect users who have enabled reduced-motion preferences.
• Fixed a build issue in ThemeToggle.tsx caused by a duplicate mounted state declaration.

Related Issue

Closes #236
also fixes #1178

Type of Contribution

• Bug fix
• New feature
• Documentation update
• Refactor
• GSSoC contribution

Participant Info

• GitHub username: gravypizza

clideo_editor_4b81878534cf4489ba484a553ccdbed2.mp4

Checklist

• I have read the contribution guidelines
• My changes follow the project structure
• I have tested my changes in Chrome, Firefox, and Safari
• bun run lint passes (repository currently contains unrelated lint issues)
• bunx tsc --noEmit passes
• New interactive elements have aria-label / accessible names
• No console.log statements left in
• This PR is related to a valid issue
• Screen recording attached above

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[github-actions]

👋 Thanks for your PR, @gravypizza!

Welcome to Reframe — a browser-based video editor built for everyone 🎬

🟠 GSSoC'26 PR detected — thanks for contributing under GirlScript Summer of Code 2026!

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• Linked the issue this PR closes (e.g. Closes #123)
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