This change adds comprehensive unit and integration tests to cover:
1. `signerKeyManager.js`: Verification of key derivation from signatures and passphrases.
2. `storageService.js`: Tests for saving, retrieving, and decrypting connections, specifically verifying that generic S3 payloads (endpoint, region, bucket) are preserved alongside R2 payloads.
3. `UploadModal.js`: Integration tests mocking the storage service to verify that R2 connection details correctly map to the UI input fields and that the "Unlock" flow updates the UI state.
It also introduces `fake-indexeddb` as a dev dependency to enable reliable testing of IndexedDB interactions in the Node/JSDOM test environment.
- Added comprehensive comments to `js/webtorrent.js` explaining the playback strategy, service worker integration, and browser-specific quirks (Brave/Firefox).
- Patched `tests/ui/helpers/jsdom-test-helpers.mjs` to expose `HTMLStyleElement` and other globals to JSDOM, fixing `ReferenceError` in UI tests.
- Fixed `tests/ui/similar-content-card.test.mjs` to align with the current component implementation (handling detached elements) and resolving environment issues.
- Updated `tests/video-modal-accessibility.test.mjs` to safely mock `navigator` and `HTMLCanvasElement.getContext`, resolving `TypeError` and "Not implemented" errors during testing.
- Exposed `HTMLStyleElement` globally in `tests/ui/popoverEngine.test.mjs` to resolve a `ReferenceError` during `instanceof` checks.
- Updated assertion in "applies token-based sizing and arrow positioning" to check the `--popover-arrow-top` CSS variable instead of the `top` property, as JSDOM does not compute layout properties from variables.
- Verified all tests in the file pass.
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