test: add 10s timeout guard across all suites

Hangs/regressions fail fast instead of stalling CI.

- shared/jest.config.js: testTimeout 10000
- src/setupTests.js: jest.setTimeout(10000) (CRA blocks testTimeout in
  package.json — not in allowlist)
- server/jest.config.js: already had 10000

Verified: injected hanging test -> 'Exceeded timeout of 10000 ms'.

shared/jest.config.js

@@ -3,4 +3,5 @@ module.exports = {
   testEnvironment: 'node',
   testMatch: ['<rootDir>/tests/**/*.test.js'],
   collectCoverageFrom: ['turn.js'],
+  testTimeout: 10000,
 };