feat: instrument personal subscription dialog + dedupe GTM event

Addresses code review:
- Add 'subscription_required_dialog' surface for the personal-tier
  SubscriptionRequiredDialogContent.vue (the dialog reached via
  showSubscriptionDialog() for non-workspace users), which was
  previously uninstrumented despite being a primary paywall path.
- Map trackPaywallViewed() in GtmTelemetryProvider to a distinct
  'paywall_viewed' GA4 event instead of 'view_promotion', which
  trackSubscription('modal_opened') already emits — avoids
  double-counting impressions on the GTM side.

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

@@ -145,7 +145,7 @@
 </template>
 
 <script setup lang="ts">
-import { computed, watch } from 'vue'
+import { computed, onMounted, watch } from 'vue'
 
 import CloudBadge from '@/components/topbar/CloudBadge.vue'
 import Button from '@/components/ui/button/Button.vue'
@@ -169,7 +169,7 @@ const emit = defineEmits<{
   close: [subscribed: boolean]
 }>()
 
-const { isActiveSubscription } = useBillingContext()
+const { isActiveSubscription, subscription } = useBillingContext()
 
 const isSubscriptionEnabled = (): boolean =>
   Boolean(isCloud && window.__CONFIG__?.subscription_required)
@@ -199,6 +199,14 @@ watch(
   }
 )
 
+onMounted(() => {
+  telemetry?.trackPaywallViewed({
+    surface: 'subscription_required_dialog',
+    current_tier: subscription.value?.tier?.toLowerCase(),
+    reason
+  })
+})
+
 const handleSubscribed = () => {
   emit('close', true)
 }

src/platform/telemetry/providers/cloud/GtmTelemetryProvider.ts

@@ -166,7 +166,7 @@ export class GtmTelemetryProvider implements TelemetryProvider {
   }
 
   trackPaywallViewed(metadata: PaywallViewedMetadata): void {
-    this.pushEvent('view_promotion', { ...metadata })
+    this.pushEvent('paywall_viewed', { ...metadata })
   }
 
   trackSignupOpened(): void {

src/platform/telemetry/types.ts

@@ -347,6 +347,7 @@ export interface SubscriptionMetadata {
  */
 export type PaywallSurface =
   | 'free_tier_dialog'
+  | 'subscription_required_dialog'
   | 'subscription_required_dialog_workspace'
   | 'upload_model_upgrade_modal'
   | 'invite_member_upsell'