chore(docs): refresh README + env.example for phases 4–5 shipped

[Copxer]

Catches up the user-facing docs after phase 4 + phase 5 closed out. No code changes.

Summary

• Phase status table flips rows 4 + 5 from ⬜ → 🟢 with one-line per-spec summaries (020–022 deployments, 023–025 monitoring).
• "What works today" gains two new sections — Phase 4 (deployments — workflow runs storage + cross-repo timeline UI with Reverb realtime + Overview success-rate widget) and Phase 5 (monitoring — CRUD + scheduled checks + uptime aggregates + Overview uptime KPI + per-website Reverb live updates).
• composer dev callout now notes the scheduler tick is what drives spec 024's monitor probes — without it (or a real cron), monitors stay on whatever state the last manual probe left them in.
• Repository layout adds the new bounded contexts + directories that shipped:
  • app/Domain/Monitoring/ (with Probes/ for the result DTO),
  • app/Events/ (the three broadcast classes — ActivityEventCreated, WorkflowRunUpserted, WebsiteCheckRecorded),
  • app/Policies/ (Project / Repository / Website),
  • Pages/Deployments/ + Pages/Monitoring/Websites/,
  • lib/workflowRunStyles.ts + lib/websiteStyles.ts (shared tone helpers).
• .env.example BROADCAST_CONNECTION comment lists all three live broadcast events instead of just spec 019. No new env keys shipped in phases 4 or 5; AGENT_SHARED_SECRET stays as the pre-seeded placeholder for phase 6.

Test plan

• No code changes — Pint / tests / build are unaffected.
• Visual scan: phase status table, "What works today" sections, repository layout diagram render correctly on GitHub.

Note

Pure documentation. Squash-merging this is fine without the usual self-review pass; the diff is two files and ~50 lines.