fix: an opencode session outside lich starts again

[omartelo]

Running opencode in a plain terminal with the plugin installed died at
startup:

Error: Unexpected server error. Check server logs for details.

The server log named the cause twice:

level=ERROR message="plugin config hook failed" error="null is not an object (evaluating 'N.config')"
level=ERROR message="Event listener failed" eventType=session.created cause="Die(TypeError: null is not an object (evaluating 'V.event'))"

Root cause

opencode loads every export of a plugin module as a plugin, not just the one
that looks like one. opencode/lich.js exported lichTools beside
LichPlugin, so opencode called it with the plugin input too — $ got the
input object, helper was undefined — and outside lich the
LICH_PORT/LICH_TOKEN/LICH_SESSION_ID guard returned null. opencode then
read hook keys off that null.

Inside lich it went unnoticed: the same call returned the tools object, whose
unknown keys opencode ignores. Only a bare terminal ever saw it.

Fix

The export existed for one reason — the suite has to inject the tool package,
because opencode resolves it from its own plugin dependencies and a checkout of
this repository has none. That seam moves onto LichPlugin's second argument,
which opencode never passes. The module is back to one export.

Test plan

• node --test tests/*.test.mjs — 127 pass
• New test loads the module the way opencode does: no lich environment,
  every export called with a plugin input, each result asserted to be a
  hooks object whose keys can be read. It fails on the export this PR
  removes (verified by re-adding the keyword).
• Isolated rig (own XDG_CONFIG_HOME/XDG_DATA_HOME, opencode 1.18.16):
  reproduced upstream by @mellow-badger — only the export keyword differs
  between the crashing and the working run.

Also cuts the release: [Unreleased] moves under v0.9.2 and both manifests
align with the tag. lich installs the module at the latest release's tag, so
the fix only reaches sessions once that release exists — tag and release to
follow the merge.