chore: sync in-progress work across marketing, admin, API and tests

Snapshot of uncommitted work that had accumulated in the tree alongside
the Turnstile changes:

- marketing pages, SEO helpers (lib/seo.ts, lib/marketing/) and
  structured data
- admin billing actions and a per-user portfolio view, plus an admin
  error boundary
- rate limiting (lib/rate-limit.ts) applied across the /api/v1 surface
- CSP and proxy adjustments, accounting/webhook lib updates
- Playwright config and an e2e/unit test suite
- next bumped to ^16.3.4 with the lockfile regenerated
- generated AGENTS.md / CLAUDE.md

Authored by other sessions working in this tree; committed here so the
Turnstile work could be pushed without leaving the tree dirty.
Typecheck passes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

package.json

@@ -11,7 +11,10 @@
     "db:generate": "drizzle-kit generate",
     "db:migrate": "drizzle-kit migrate",
     "db:push": "drizzle-kit push",
-    "db:studio": "drizzle-kit studio"
+    "db:studio": "drizzle-kit studio",
+    "test": "playwright test --project=unit",
+    "test:unit": "playwright test --project=unit",
+    "test:e2e": "playwright test --project=e2e"
   },
   "dependencies": {
     "@anthropic-ai/sdk": "^0.110.0",
@@ -25,7 +28,7 @@
     "@radix-ui/react-switch": "^1.2.6",
     "@sentry/nextjs": "^10.63.0",
     "@types/papaparse": "^5.5.2",
-    "better-auth": "^1.6.20",
+    "better-auth": "^1.7.2",
     "clsx": "^2.1.1",
     "date-fns": "^4.1.0",
     "dotenv": "^17.4.2",
@@ -34,7 +37,7 @@
     "jspdf": "^4.2.1",
     "leaflet": "^1.9.4",
     "lucide-react": "^1.7.0",
-    "next": "16.2.2",
+    "next": "^16.3.4",
     "nodemailer": "^9.0.3",
     "openai": "^6.33.0",
     "papaparse": "^5.5.3",
@@ -58,7 +61,7 @@
     "@types/react-dom": "^19",
     "drizzle-kit": "^0.31.10",
     "eslint": "^9",
-    "eslint-config-next": "16.2.2",
+    "eslint-config-next": "^16.3.4",
     "tailwindcss": "^4",
     "typescript": "^5"
   }