feat(mod): report compacting while Claude Code compacts the conversation

[omartelo]

Client side of the session-state contract's new compacting state (lichdotdev/lich#687).

What

hooks/mod-compacting.js (registered by hooks/lich.js) brackets session.compact:
compacting before the compaction runs, then the state the session returns to once
next(e) settles, whether it resolved or rejected. A manual /compact closes with
done, an automatic one with busy, because its turn is still running and the turn's
own Stop reports done. Only the manual and auto triggers are hooked, each through
its own matcher. A subagent's compaction (agentId) is passed through, and so is a
non-interactive run.

Measured (Claude Code 2.1.295, interactive PTY, stub lich)

• session.compact: {trigger: "manual"|"auto", messages}. next(e) resolves to
  {messages} after the summary (manual ~6s, auto ~14s).
• Esc on /compact makes next(e) reject with "Request was aborted". An auto
  compaction the engine gives up on rejects within ~40ms with "reactive compaction
  did not settle ok", and the turn continues. PostCompact fires in neither case,
  which is why this is a mod and not a settings hook.
• Before this, a manual /compact left the card on done (no UserPromptSubmit),
  and an auto compaction showed a bare spinner.
• Live run with this branch: manual gives compacting → done; auto gives
  busy → compacting → busy → done.

Discarded

• session.end (reason): the existing SessionEnd → idle already covers /clear,
  /resume, /branch and exit. Claude Code awaits it before SessionStart, so idle
  always lands before the new /session-start id, and the card ends up right.
• session.attach/detach: never fired in a PTY session. Tested with Remote
  Control opened from claude.ai. Only a stream-json ui_attach from a remote
  render surface raises it.

Notes for review

• tests/lich-ref stays at v0.61.0. tests/refresh-fixtures.sh reads session-state.jsonl
  alone at f4481848, the commit where feat: show a Claude Code card's compaction as "Compacting..." lich#687 was merged into lich's main and
  which no release includes yet. Once a lich release includes that merge, move
  lich-ref to that release and put the file back in the loop.
• Two assertions in tests/hooks.test.mjs pinned the old state vocabulary. They
  now expect compacting in the fixtures, and scripts are no longer expected to
  register it, since Claude Code reports it from the mod and no other harness
  reports it.
• The release that carries this must be a minor (lich raised its plugin ceiling
  to 0.20.0). There is no version bump here.

node --test tests/*.test.mjs: 356/356. claude plugin validate .claude-plugin/plugin.json: passes; the warnings are the "gating hook without .catch" ones the other mods already have.