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>

lib/seo.ts

@@ -0,0 +1,71 @@
+import type { Metadata } from "next"
+
+export const SITE_NAME = "Property Management Network"
+
+// The generated Open Graph card (app/opengraph-image.tsx), served at this path.
+// Declared explicitly because a page that sets its own `openGraph` object
+// replaces the inherited one — including the image Next.js attaches from the
+// file convention — which silently leaves that page with no share image.
+const OG_IMAGE = "/opengraph-image"
+
+type PageSeo = {
+  /**
+   * Page title. Rendered through the root layout's "%s | Property Management
+   * Network" template unless `absoluteTitle` is set.
+   */
+  title: string
+  /** Render `title` verbatim, without the site-name suffix. */
+  absoluteTitle?: boolean
+  description: string
+  /** Canonical path, root-relative and without a trailing slash, e.g. "/terms". */
+  path: string
+  /**
+   * Headline used for the Open Graph / Twitter card when the share copy should
+   * differ from the page title. Defaults to the resolved page title.
+   */
+  socialTitle?: string
+  /** Set false for pages that must stay out of the index. */
+  index?: boolean
+}
+
+/**
+ * Builds a complete, self-consistent metadata block for a public page.
+ *
+ * Every public page must go through this helper so that canonical, og:url,
+ * og:title, og:image and the Twitter card always agree with each other and with
+ * the page's real URL. Setting these ad hoc per page is what previously left the
+ * landing page with no share image and every legal page pointing og:url at "/".
+ */
+export function pageMetadata({
+  title,
+  absoluteTitle = false,
+  description,
+  path,
+  socialTitle,
+  index = true,
+}: PageSeo): Metadata {
+  const fullTitle = absoluteTitle ? title : `${title} | ${SITE_NAME}`
+  const social = socialTitle ?? fullTitle
+
+  return {
+    title: absoluteTitle ? { absolute: title } : title,
+    description,
+    alternates: { canonical: path },
+    openGraph: {
+      title: social,
+      description,
+      url: path,
+      siteName: SITE_NAME,
+      locale: "en_US",
+      type: "website",
+      images: [OG_IMAGE],
+    },
+    twitter: {
+      card: "summary_large_image",
+      title: social,
+      description,
+      images: [OG_IMAGE],
+    },
+    ...(index ? {} : { robots: { index: false, follow: true } }),
+  }
+}