feat: launch Stripe billing flows with lifecycle hardening and analytics

add Stripe checkout, portal, webhook ingestion, and idempotent event persistence

add billing lifecycle state (grace/sync/timeline/admin visibility) and stronger entitlement handling

add analytics event tracking and admin summary APIs plus account/pricing UI integration

package.json

@@ -38,6 +38,7 @@
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "stream-json": "^2.1.0",
+    "stripe": "^22.1.1",
     "tailwind-merge": "^3.5.0",
     "vite": "^6.2.0",
     "zod": "^4.3.6"