Migrate to Vite & Upgrade Pdf.js

[JSv4]

To derisk big upgrade of pdf.js, I wanted Playwright coverage to ensure basic functionality didn't break. This was a lot easier with Vite. So this PR:

1. Adds Vite
2. Adds Playwright and basic test for DocumentKnowledgeBase.tsx
3. Upgrades pdf.js

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.96%. Comparing base (9744b94) to head (dfd0f1e).
Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #353   +/-   ##
=======================================
  Coverage   89.96%   89.96%           
=======================================
  Files         280      280           
  Lines       12816    12816           
=======================================
  Hits        11530    11530           
  Misses       1286     1286           

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