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/upload/route.ts

@@ -9,6 +9,7 @@ import {
   extOf,
 } from "@/lib/storage"
 import { checkStorageLimit } from "@/lib/plan-limits"
+import { enforceRateLimit } from "@/lib/rate-limit"
 
 const ALLOWED_SCOPES = ["property-images", "maintenance", "documents", "misc"]
 
@@ -24,6 +25,11 @@ export async function POST(request: Request) {
   if (!ctx.canWrite) return NextResponse.json({ error: "Forbidden" }, { status: 403 })
   const ownerId = ctx.ownerId
 
+  // Storage quota caps total bytes, but not the rate of writes — throttle so a
+  // single account cannot hammer Spaces (or fill a plan's quota) in one burst.
+  const limited = enforceRateLimit(`upload:${ownerId}`, 60, 60)
+  if (limited) return limited
+
   const fd = await request.formData()
   const file = fd.get("file") as File | null
   const scopeRaw = (fd.get("scope") as string) || "misc"