feat: add custom export presets

[Abhi190702]

PR.recording.1.mp4

Summary

Fixes #683

Adds custom export presets so users can save their current EditRecipe with a name and reuse it later.

What Changed

• Added custom preset persistence with localStorage
• Split built-in presets from custom preset handling
• Added a “Save preset” button near the preset selector
• Added a modal for naming custom presets
• Added a “Custom” section below built-in presets
• Added delete buttons for individual custom presets
• Enforced a max of 10 custom presets with a helpful message
• Updated export and preview dimension resolution so saved custom preset IDs restore the correct dimensions
• Added tests for built-in vs custom preset dimension lookup

Testing

• bun test
• bun run build
• Custom preset can be saved
• Custom preset appears under Custom section
• Custom preset persists after reload
• Selecting custom preset restores saved settings
• Custom preset can be deleted
• Max 10 custom presets message appears

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👋 Thanks for your PR, @Abhi190702!

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Quick checklist

• PR title follows Conventional Commits (e.g. feat: add dark mode)
• Linked the issue this PR closes (e.g. Closes #123)
• Tested the changes locally (bun run dev)
• Build passes (bun run build)

Useful links

• 📖 CONTRIBUTING.md
• 🐛 Open Issues
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Happy coding! 🎉

[Abhi190702]

@magic-peach , I will upload the following screenrecording soon