[app-cli] Document events.jsonl (`amplifier.log` schema) as a stable, versioned integration surface

Context. Each session's events.jsonl (written by the hooks-logging module) is the best available signal for external tools to track session lifecycle: every record carries {"schema": {"name": "amplifier.log", "ver": "1.0.0"}, "event", "session_id", "ts", "data"}, and the lifecycle events (session:start, session:config, prompt:submit, execution:start/end, prompt:complete, session:resume, session:end) are exactly what a supervisor needs for busy/idle state and turn-completion notifications. We now drive a terminal-manager integration entirely from this file (danshapiro/freshell#514) — it's dramatically more reliable than inferring turn state from terminal output timing.

Ask.

1. Document the amplifier.log record shape and the lifecycle event vocabulary as a supported integration surface (even with an "additive changes within major version 1" caveat).
2. Commit to major-version discipline: bump schema.ver major on breaking changes so consumers can gate safely.
3. Note event-ordering caveats in the docs (we observed records near shutdown appearing out of timestamp order, and background session-naming llm:request/provider:retry records after prompt:complete — both fine, but worth documenting).

Start by reading the hooks-logging module and the events.jsonl records described in the issue, focusing on the amplifier.log schema and listed lifecycle events. Document the record shape, additive version-1 policy, major-version rule, and observed ordering caveats; done means external consumers can understand and safely gate the integration.