Add Claude and Codex usage tracking from status lines for better budget estimates

[akhilsinghcodes]

This PR adds best-effort usage tracking for interactive agent sessions by parsing Claude Code and Codex status-line output in PTY streams.

What changed

• Added parsing logic in apps/server/src/processManager.ts for:
  • Claude status-line output
  • Codex token usage/status output
• Extended shared websocket message types in packages/shared/src/index.ts to support usage tick events.
• Added UI support in apps/web/src/TerminalPane.tsx to surface live usage tracking updates.
• Updated README.md with setup instructions for:
  • Claude Code status line configuration
  • Codex status line configuration

Why

Agents Fleet previously relied on rough token/cost estimation for PTY sessions. This change improves accuracy by reading usage data directly from the agent CLIs when available, which helps with:

• better budget enforcement
• more accurate cost estimates
• clearer live session visibility