Fix YouTube arrow seek speed reset

[sharno]

Summary:

• Only treat unhandled keyboard gestures as native speed changes for speed shortcut keys like < and >.
• Keep YouTube arrow-key seeking from accepting a transient 1x reset as user intent.
• Add regression coverage for arrow seek reset and native speed shortcuts.

Tests:

• npm test -- tests/unit/utils/event-manager.test.js
• npm run test:unit
• npm test
• npx eslint "src//*.js" "tests//*.js"
• npm run build
• node tests/e2e/run-e2e.js youtube