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>

app/(marketing)/privacy/page.tsx

@@ -1,12 +1,12 @@
 import { LegalPage, Section, Callout, LegalContact } from "@/components/marketing/legal"
 import { LEGAL, SUBPROCESSORS } from "@/lib/legal"
+import { pageMetadata } from "@/lib/seo"
 
-export const metadata = {
+export const metadata = pageMetadata({
   title: "Privacy Policy",
-  description:
-    "How we collect, use, share, and protect personal data, and the privacy rights available to you under the GDPR and California law.",
-  alternates: { canonical: "/privacy" },
-}
+  description: "How we collect, use, share, and protect personal data, and the privacy rights available to you under the GDPR and California law.",
+  path: "/privacy",
+})
 
 export default function Page() {
   return (