chore(billing): drop inert density attr on pricing toggle (no-op prop)

Phase 0 nit — BillingPricingToggleComponent has no density prop; the binding
falls through as inert HTML attribute on the root div with no effect.
Remove the binding (Vuetify density is not surfaced by this wrapper).

Author: PierreBrisorgueil

src/modules/billing/views/billing.pricing.view.vue

@@ -55,7 +55,6 @@
             :annual="annual"
             :disabled="activeTab === 1"
             class="mb-8"
-            density="compact"
             data-test="pricing-toggle"
             @update:annual="annual = $event"
           />