refactor(telemetry): drop plugin_loaded capture from plugin entry

src/index.telemetry.test.ts

@@ -34,8 +34,6 @@ const mockCreatePluginPostHog = mock(() => ({
   trackActive: () => {
     throw new Error("telemetry failed")
   },
-  capture: mock(() => {}),
-  captureException: mock(() => {}),
   shutdown: mock(async () => {}),
 }))
 const mockGetPostHogDistinctId = mock(() => "plugin-distinct-id")
@@ -104,12 +102,6 @@ function installModuleMocks(): void {
     createPluginPostHog: mockCreatePluginPostHog,
     getPostHogDistinctId: mockGetPostHogDistinctId,
   }))
-  mock.module("./shared/posthog-activity-state", () => ({
-    getPluginLoadedCaptureState: () => ({
-      dayUTC: "2026-04-18",
-      capturePluginLoaded: true,
-    }),
-  }))
 }
 
 describe("oh-my-openagent telemetry isolation", () => {