fix(desktop): split pending idle sessions

[laxmanclo]

Summary

• rename the Electron board's first column from Working to Pending
• split that existing first column into Working and Idle subsections without adding extra columns
• show idle cards with an Idle badge instead of Working
• add a renderer integration check for active vs idle placement

Checks

• npm run test -- src/renderer/tests/integration/pr-hydration.test.tsx
• npx prettier --check src/renderer/components/SessionsBoard.tsx src/renderer/tests/integration/pr-hydration.test.tsx

Note

• npm run typecheck is currently blocked on latest main by forge.config.ts(33,51): Property osxNotarize does not exist on type ForgePackagerOptions | undefined; this PR does not touch that config.