test(upload): add unit tests for useVideoUpload hook

[DSanich]

Summary

• Add src/hooks/useVideoUpload.test.ts with 21 unit tests covering the full video upload pipeline
• Tests lock in current MVP behaviour (single-segment upload, first-clip-only fallback for multi-segment) to serve as a regression baseline for future multi-clip concatenation work

Avoid naming corporate partners, customers, or other sensitive external brands in this PR title or body. Use generic descriptors unless a maintainer explicitly approves the public reference.

Motivation

• useVideoUpload is a critical hook responsible for combining recorded segments, extracting video duration, uploading to the media server, tracking progress, and showing toast notifications — yet it had zero test coverage
• Without tests, regressions in the upload pipeline are silent and only discoverable at runtime
• These tests also formally document the known MVP limitation in combineSegments (multi-segment → first clip only), so any future change to that behaviour will be caught immediately

Related Issue

• Closes test(upload): add unit tests for useVideoUpload hook #295

Testing

• npm run test
• Manual verification completed

Visuals

• No visual change
• Visuals and text avoid sensitive external brand or partner names unless explicitly approved

[github-actions]

🚀 Preview Deployment

Property	Value
Preview URL	https://4925c5a5.divine-web-fm8.pages.dev
Commit	090e4b7
Branch	feat/295-add-unit-tests-for-useVideoUpload-hook