test(extension): isolate background reconnect timers

[jackwener]

Summary

• Keep the default background startup daemon ping pending in tests unless a test explicitly controls it
• Clear pending timers after each background test so reconnect timers cannot leak into later tests

Verification

• npm run test -- --project extension extension/src/background.test.ts
• npx vitest run --project extension extension/src/
• npm run typecheck
• npm run build
• cd extension && npm run build
• HOME=$(mktemp -d) npm test