feat(plugin): push plugin runtime ops samples to the Space control plane

The shared Cloud deployment runs one Plugin Runtime for every Workspace, but
nothing reported its health: the instance only exposed two aggregate numbers on
its own health probe, and the per-installation failure registry, the desired
state registry and the reconcile outcome lived in memory with no reader.

Add RuntimeOpsReporter, which every 30 seconds reads the Runtime ``/healthz``
probe over HTTP (derived from ``plugin.runtime_ws_url``), merges it with the
connector's desired-state, failure and reconcile summaries, and posts one
sample to the Space control plane on the existing authenticated direction.
Delivery is best-effort and bounded: a single in-flight request, a ten second
timeout, dropped samples counted in ``runtime_ops`` on the instance health
probe, and a failed probe recorded as a drop so the dashboard shows staleness
instead of grading a stale sample as healthy.

Cloud-only: a non-cloud deployment never enables the reporter, and the channel
is independent of product telemetry so ``space.disable_telemetry`` cannot blind
the ops dashboard.

src/langbot/pkg/core/app.py

@@ -304,6 +304,11 @@ class Application:
         if callable(database_snapshot):
             database_stats = database_snapshot()
 
+        runtime_ops_stats = {}
+        runtime_ops_reporter = getattr(self.plugin_connector, 'runtime_ops_reporter', None)
+        if runtime_ops_reporter is not None:
+            runtime_ops_stats = runtime_ops_reporter.get_stats()
+
         return {
             'asyncio_tasks': asyncio_tasks,
             'event_loop': self.event_loop_monitor.snapshot(),
@@ -314,6 +319,7 @@ class Application:
             'query_pool': query_pool_stats,
             'models': model_stats,
             'runtimes': runtime_stats,
+            'runtime_ops': runtime_ops_stats,
             'telemetry_tasks': len(getattr(self.telemetry, 'send_tasks', ())),
         }