fix(plugin): lift calendarScheduler to module scope (multi-register singleton)

Trying the prior multi-agent-handle fix in dind-t2 surfaced a second bug
that PR #7 didn't reach: `harborforge_calendar_status` still returned
`Calendar scheduler not running` even though the gateway log showed the
scheduler had started 30+ seconds before the agent's call.

## Root cause

`register()` is invoked once per agent — `grep -c "HarborForge plugin
registered" /tmp/gw-stdout.log` reports 5 for a 5-agent claw. Every
invocation creates its own `let calendarScheduler` closure binding. But
`gateway_start` fires once and we only call `startCalendarScheduler()`
through that single hook, so exactly one of the five closures sees the
handle and the other four keep their bindings at `null`.

The host's tool router picks one of the five duplicate
`harborforge_calendar_status` registrations to dispatch to — most of the
time it's one of the four "null" closures, which is why every wakeup the
agent saw `Calendar scheduler not running`.

## Fix

Lift `let calendarScheduler` out of `register()` and into module scope.
All five register-call closures now reference the same binding; once the
single `gateway_start` initialises it, every tool sees it.

`startCalendarScheduler()` now early-returns when `calendarScheduler` is
already set, so duplicate `gateway_start` firings (if the host ever does
that) don't double-install intervals.

Bumps version 0.3.2 → 0.3.3.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugin/package.json

@@ -1,6 +1,6 @@
 {
   "name": "harbor-forge-plugin",
-  "version": "0.3.2",
+  "version": "0.3.3",
   "description": "OpenClaw plugin for HarborForge monitor bridge and CLI integration",
   "type": "module",
   "main": "dist/index.js",