Fix custom Agent label reconciliation

[OldKrab]

Summary

• preserve a resolved custom Agent label when a context-free full Task response falls back to the raw Agent id
• keep authoritative labels and changed Agent bindings eligible to replace prior presentation
• cover the auto-approve mutation response that exposed the regression

Tests

• npm run check --workspace packages/frontend
• npm test --workspace packages/frontend -- --run src/state/appReducer.test.ts src/intents/taskMutationIntents.test.ts src/components/TaskView.presentation.test.tsx src/state/appServerProtocolMapping.test.ts (180 passed)
• npm test --workspace packages/frontend (1314 passed; unrelated App.test.tsx import/build test timed out at 5 seconds)
• npm test --workspace packages/frontend -- --run src/components/App.test.tsx -t "reserves the New Task status for task-level progress" (passed in isolation)