IRCX v1.4.0 - agent can see channel events (joins/parts/quits)

The agent can now see who comes and goes in its channels - joins, parts, quits, kicks, and nick changes - not just messages.

✨ What's new

Set IRCX_SHOW_EVENTS=true (default off) and the bot records membership events into each channel's rolling context buffer (and the on-disk log), so they show up in channel_context on the next turn. Now the agent can greet a returning friend, notice someone left, or follow a nick change.

Event	Recorded as
join	*** alice has joined #chan
part	*** alice has left #chan (reason)
quit	*** alice has quit IRC (reason) - to every channel shared with the bot
kick	*** bob was kicked from #chan by alice (reason)
nick	*** alice is now known as alice2 - to every shared channel

🔒 Design / safety

• Pure visibility: events are context only - never dispatched as a prompt, so no reply storms.
• The bot's own joins/parts are skipped.
• Quits/nick-changes are attributed correctly across channels: shared membership is snapshotted before parse_tokens removes/renames the user.
• Respects group_policy: allowlist and the on-disk logging setting.
• Off by default - it's noisy on large channels; enable per deployment.

✅ Tests

9 new tests; full IRCX suite 141 passing, no regressions. CI green.