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/main.ts

@@ -30,6 +30,9 @@ if (isCloud) {
   const { refreshRemoteConfig } =
     await import('@/platform/remoteConfig/refreshRemoteConfig')
   await refreshRemoteConfig({ useAuth: false })
+
+  const { initGtm } = await import('@/platform/telemetry/gtm')
+  initGtm()
 }
 
 const ComfyUIPreset = definePreset(Aura, {