feat: add cloud gtm injection (#8311)

## Summary

Add GTM injection for cloud distribution builds and push SPA page view +
signup events.

## Changes

- **What**: Inject GTM script into head-prepend and noscript iframe into
body-prepend for cloud builds
- **What**: Push `page_view` to `dataLayer` on cloud route changes
(page_location + page_title)
- **What**: Push `sign_up` to `dataLayer` after successful account
creation (email/google/github)
- **Dependencies**: None

## Review Focus

- Placement order for head-prepend/body-prepend and cloud-only gating
- Route-change page_view payload shape
- Signup event emission only for new users

## Screenshots (if applicable)

<img width="1512" height="860" alt="Screenshot 2026-01-26 at 11 38
11 AM"
src="https://github.com/user-attachments/assets/03fb61db-5ca4-4432-9704-bbdcc4c6c1b7"
/>

<img width="1512" height="862" alt="Screenshot 2026-01-26 at 11 38
26 AM"
src="https://github.com/user-attachments/assets/6e46c855-a552-4e52-9800-17898a512d4d"
/>

src/router.ts

@@ -9,6 +9,7 @@ import type { RouteLocationNormalized } from 'vue-router'
 
 import { useFeatureFlags } from '@/composables/useFeatureFlags'
 import { isCloud } from '@/platform/distribution/types'
+import { pushDataLayerEvent } from '@/platform/telemetry/gtm'
 import { useDialogService } from '@/services/dialogService'
 import { useFirebaseAuthStore } from '@/stores/firebaseAuthStore'
 import { useUserStore } from '@/stores/userStore'
@@ -36,6 +37,16 @@ function getBasePath(): string {
 
 const basePath = getBasePath()
 
+function pushPageView(): void {
+  if (!isCloud || typeof window === 'undefined') return
+
+  pushDataLayerEvent({
+    event: 'page_view',
+    page_location: window.location.href,
+    page_title: document.title
+  })
+}
+
 const router = createRouter({
   history: isFileProtocol
     ? createWebHashHistory()
@@ -93,6 +104,10 @@ installPreservedQueryTracker(router, [
   }
 ])
 
+router.afterEach(() => {
+  pushPageView()
+})
+
 if (isCloud) {
   const { flags } = useFeatureFlags()
   const PUBLIC_ROUTE_NAMES = new Set([