[billing] #11 Billing page #3715

Context

Authenticated page for org members to view and manage their subscription.

Scope

• src/modules/billing/views/Billing.view.vue — current plan, status, next billing date, manage/upgrade buttons
• src/modules/billing/components/PlanBadge.component.vue — visual badge (Free/Starter/Pro)
• "Manage Subscription" → calls billingStore.openPortal() → Stripe Customer Portal
• "Upgrade" → navigates to /pricing
• Route: meta.requiresAuth: true

Acceptance criteria

• /billing shows current org subscription details
• "Manage" opens Stripe Customer Portal
• "Upgrade" navigates to pricing page
• Unauthenticated users redirected to signin

Dependencies

• [billing] ci(travis): improve deploy script 👷🏼 #8 (store + router)