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/api/v1/webhooks/route.ts

@@ -3,6 +3,7 @@ import { desc, eq } from "drizzle-orm"
 import { db } from "@/lib/db"
 import { webhook_endpoints } from "@/lib/db/schema"
 import { resolveApiRequest } from "@/lib/api-auth"
+import { enforceRateLimit } from "@/lib/rate-limit"
 import { webhookEndpointSchema } from "@/lib/validations"
 import { isWebhookEvent } from "@/lib/webhooks/events"
 import { assertSafeWebhookUrl, WebhookUrlError } from "@/lib/webhooks/ssrf"
@@ -37,6 +38,10 @@ export async function GET(request: Request) {
   const ctx = await resolveApiRequest(request)
   if (!ctx) return unauthorized()
 
+  // Public API budget: 120 requests/minute per key owner.
+  const limited = enforceRateLimit(`v1:${ctx.userId}`, 120, 60)
+  if (limited) return limited
+
   const data = await db
     .select(PUBLIC_COLUMNS)
     .from(webhook_endpoints)
@@ -49,6 +54,10 @@ export async function GET(request: Request) {
 export async function POST(request: Request) {
   const ctx = await resolveApiRequest(request)
   if (!ctx) return unauthorized()
+
+  // Public API budget: 120 requests/minute per key owner.
+  const limited = enforceRateLimit(`v1:${ctx.userId}`, 120, 60)
+  if (limited) return limited
   if (!ctx.canWrite) return forbidden()
 
   const body = await request.json().catch(() => null)