feat(budget): add Dune UI for token budget controls

[DorianZheng]

Summary

• BudgetSettings.tsx: per-agent budget config form in settings
• BudgetExceededBanner.tsx: red banner with Resume button when agent is paused
• BudgetWarningBadge.tsx: yellow badge at >=80% usage
• AgentPanel.tsx: integrates banner + badge, subscribes to budget events
• IPC plumbing: getBudget, setBudget, resumeBudget, budget event subscriptions

Test plan

• Set a $0.001 limit in Budget settings, trigger agent, verify pause + banner
• Click Resume, verify agent runs again
• Set 80% threshold budget, verify warning badge appears
• TypeScript compiles cleanly

🤖 Generated with Codex (AgentLite Developer 4)