fix(telemetry): dedupe plugin_loaded event to once per UTC day

The plugin_loaded event was emitted on every plugin reload, generating
high event volume on PostHog (proportional to opencode restarts per
user per day). With MAU > 60K and active power users restarting
frequently, this drove unnecessary event spend.

Add a separate daily dedup state field (lastPluginLoadedDayUTC) so the
plugin_loaded capture only fires once per UTC day per machine. The
existing daily activity dedup (lastActiveDayUTC, used by
omo_daily_active) is preserved as an independent gate so the two
dimensions cannot overwrite each other in the activity state file.

src/shared/posthog-activity-state.ts

@@ -8,6 +8,7 @@ import { writeFileAtomically } from "./write-file-atomically"
 
 type PostHogActivityState = {
   lastActiveDayUTC?: string
+  lastPluginLoadedDayUTC?: string
 }
 
 type PostHogActivityCaptureState = {
@@ -15,6 +16,11 @@ type PostHogActivityCaptureState = {
   captureDaily: boolean
 }
 
+type PluginLoadedCaptureState = {
+  dayUTC: string
+  capturePluginLoaded: boolean
+}
+
 const POSTHOG_ACTIVITY_STATE_FILE = "posthog-activity.json"
 
 function getPostHogActivityStateFilePath(): string {
@@ -73,7 +79,8 @@ export function getPostHogActivityCaptureState(now: Date = new Date()): PostHogA
 
   if (captureDaily) {
     writePostHogActivityState({
-      lastActiveDayUTC: captureDaily ? dayUTC : state.lastActiveDayUTC,
+      ...state,
+      lastActiveDayUTC: dayUTC,
     })
   }
 
@@ -82,3 +89,22 @@ export function getPostHogActivityCaptureState(now: Date = new Date()): PostHogA
     captureDaily,
   }
 }
+
+export function getPluginLoadedCaptureState(now: Date = new Date()): PluginLoadedCaptureState {
+  const state = readPostHogActivityState()
+  const dayUTC = getUtcDayString(now)
+
+  const capturePluginLoaded = state.lastPluginLoadedDayUTC !== dayUTC
+
+  if (capturePluginLoaded) {
+    writePostHogActivityState({
+      ...state,
+      lastPluginLoadedDayUTC: dayUTC,
+    })
+  }
+
+  return {
+    dayUTC,
+    capturePluginLoaded,
+  }
+}