feat: integrate Impact telemetry with checkout attribution for subscriptions (#8688)

Implement Impact telemetry and checkout attribution through cloud
subscription checkout flows.

This PR adds Impact.com tracking support and carries attribution context
from landing-page visits into subscription checkout requests so
conversion attribution can be validated end-to-end.

- Register a new `ImpactTelemetryProvider` during cloud telemetry
initialization.
- Initialize the Impact queue/runtime (`ire`) and load the Universal
Tracking Tag script once.
- Invoke `ire('identify', ...)` on page views with dynamic `customerId`
and SHA-1 `customerEmail` (or empty strings when unknown).
- Expand checkout attribution capture to include `im_ref`, UTM fields,
and Google click IDs, with local persistence across navigation.
- Attempt `ire('generateClickId')` with a timeout and fall back to
URL/local attribution when unavailable.
- Include attribution payloads in checkout creation requests for both:
  - `/customers/cloud-subscription-checkout`
  - `/customers/cloud-subscription-checkout/{tier}`
- Extend begin-checkout telemetry metadata typing to include attribution
fields.
- Add focused unit coverage for provider behavior, attribution
persistence/fallback logic, and checkout request payloads.

Tradeoffs / constraints:
- Attribution collection is treated as best-effort in tiered checkout
flow to avoid blocking purchases.
- Backend checkout handlers must accept and process the additional JSON
attribution fields.

## Screenshots

<img width="908" height="208" alt="image"
src="https://github.com/user-attachments/assets/03c16d60-ffda-40c9-9bd6-8914d841be50"/>
<img width="1144" height="460" alt="image"
src="https://github.com/user-attachments/assets/74b97fde-ce0a-43e6-838e-9a4aba484488"/>
<img width="1432" height="320" alt="image"
src="https://github.com/user-attachments/assets/30c22a9f-7bd8-409f-b0ef-e4d02343780a"/>
<img width="341" height="135" alt="image"
src="https://github.com/user-attachments/assets/f6d918ae-5f80-45e0-855a-601abea61dec"/>

src/platform/cloud/subscription/components/PricingTable.vue

@@ -267,7 +267,7 @@ import { isPlanDowngrade } from '@/platform/cloud/subscription/utils/subscriptio
 import type { BillingCycle } from '@/platform/cloud/subscription/utils/subscriptionTierRank'
 import { isCloud } from '@/platform/distribution/types'
 import { useTelemetry } from '@/platform/telemetry'
-import { getCheckoutAttribution } from '@/platform/telemetry/utils/checkoutAttribution'
+import type { CheckoutAttributionMetadata } from '@/platform/telemetry/types'
 import { useFirebaseAuthStore } from '@/stores/firebaseAuthStore'
 import type { components } from '@/types/comfyRegistryTypes'
 
@@ -280,6 +280,19 @@ const getCheckoutTier = (
   billingCycle: BillingCycle
 ): CheckoutTier => (billingCycle === 'yearly' ? `${tierKey}-yearly` : tierKey)
 
+const getCheckoutAttributionForCloud =
+  async (): Promise<CheckoutAttributionMetadata> => {
+    // eslint-disable-next-line no-undef
+    if (__DISTRIBUTION__ !== 'cloud') {
+      return {}
+    }
+
+    const { getCheckoutAttribution } =
+      await import('@/platform/telemetry/utils/checkoutAttribution')
+
+    return getCheckoutAttribution()
+  }
+
 interface BillingCycleOption {
   label: string
   value: BillingCycle
@@ -415,7 +428,7 @@ const handleSubscribe = wrapWithErrorHandlingAsync(
 
     try {
       if (isActiveSubscription.value) {
-        const checkoutAttribution = getCheckoutAttribution()
+        const checkoutAttribution = await getCheckoutAttributionForCloud()
         if (userId.value) {
           telemetry?.trackBeginCheckout({
             user_id: userId.value,