Extract StatusState from AppLayout to constructor injection

[shellicar]

Summary

• StatusState was the only state class updated from outside AppLayout, routed through setModel and updateUsage on the layout
• Moved construction to main.ts; passed directly to AppLayout and AgentMessageHandler
• Removed AppLayout.setModel and AppLayout.updateUsage; callers now write to the state object directly
• Test updated to assert on StatusState fields rather than mocking layout methods

[bananabot9000]

Phase 2 clean. StatusState extracted to constructor injection, proxy methods deleted, callers talk to state directly. Test verifies actual state instead of mock call counts. Testament is signal-only -- verification results + biome side-effect + staging instruction. No suspicious files. 🍌