Mock video fetching for Cypress tests

[dan-niles]

Fix #245

• Added code to intercept the video loading in video.js during the Cypress tests and play a mock video instead.
• Added a sample video in the Cypress fixtures folder.
• Added placeholders for profile pic and video thumbnails.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 1.62%. Comparing base (d56c272) to head (71928dd).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #246 +/- ## ===================================== Coverage 1.62% 1.62% ===================================== Files 11 11 Lines 1047 1047 Branches 158 158 ===================================== Hits 17 17 Misses 1030 1030 ```

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