feat: add agent activity status files

[DorianZheng]

Summary

• add src/agent/status-writer.ts with the status schema, atomic file writes, and tool argument summaries
• instrument ActionsHttp to write status updates before and after tool calls, including terminal done and error states
• wire AgentImpl to create per-session status metadata and write terminal status on shutdown
• make GitHub/git installs run build during prepare so fresh installs generate the required dist/ output
• add focused tests for status writing and action HTTP instrumentation

Validation

• pnpm run build
• pnpm exec vitest run src/agent/status-writer.test.ts src/agent/actions-http.test.ts
• clean temp install of @boxlite-ai/agentlite@github:boxlite-ai/agentlite#54e4a4edf8e852fa96d72736ca834fed15616be7 and verification that the installed dist/agent output contains the observability code