Fix Shorts support and add userscript voting

Harden Shorts controls, reaction state, and navigation; share voting logic
with the extension; improve ratio-bar rendering; and add comprehensive Jest,
Playwright, artifact, and live-browser regression coverage.

jest.config.js

@@ -2,7 +2,10 @@ module.exports = {
   resetMocks: true,
   collectCoverage: false,
   collectCoverageFrom: [
+    "Extensions/common/**/*.js",
     "Extensions/combined/src/**/*.js",
     "Extensions/combined/*.js",
+    "Extensions/UserScript/src/**/*.js",
   ],
+  testPathIgnorePatterns: ["/node_modules/", "<rootDir>/Extensions/UserScript/e2e/"],
 };