feat: auto-save user editing session and video to IndexedDB

[AdityaM-IITH]

Description

Implements an aggressive session-restoration feature that preserves the user's uploaded video file across browser refreshes and accidental page reloads.

• Added sessionDB.ts: A lightweight wrapper around IndexedDB for securely caching the File blob locally.
• useVideoEditor.ts: Hooked into IndexedDB on mount to seamlessly restore the video blob into the state without overwriting the user's persisted recipe settings.
• VideoEditor.tsx: Renamed the generic "Reset all settings" button to "Clear saved session" to match the feature request, wiring it up to purge both localStorage and IndexedDB when clicked.

Related Issue

Fixes #1540

Type of Contribution

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

Participant Info

• GitHub username: @AdityaM-IITH
• Contribution level (Beginner/Intermediate/Advanced): Advanced

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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 (no ESLint errors)
• bunx tsc --noEmit passes (no TypeScript errors)
• 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 (required for UI/feature/design changes)

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[github-actions]

👋 Thanks for your PR, @AdityaM-IITH!

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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[github-actions]

✅ PR Format Check Passed — @AdityaM-IITH

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