feat: Cloudflare Turnstile on auth, CSP fixes, admin/SEO/analytics additions

Turnstile bot protection (sign-in, sign-up, password-reset):
- Register Better Auth's captcha plugin with the cloudflare-turnstile
  provider; endpoints listed explicitly rather than relying on defaults.
  /reset-password is intentionally excluded — it is reached only via a
  single-use emailed token.
- Add an explicit-render Turnstile widget component. Tokens are single-use,
  so each form resets the challenge after a failed submit; submit stays
  disabled until a token is held.
- Read the site key server-side and pass it down as a prop, so rotating it
  does not require a rebuild.
- Fail fast in production when TURNSTILE_SECRET_KEY is missing, and when a
  secret is set without a site key (that combination would demand a token
  no form can produce, locking every user out).
- Pass a throwaway secret during `next build` in the Dockerfile, mirroring
  the existing BETTER_AUTH_SECRET treatment, so image builds don't need it.

CSP fixes in middleware (these blocked Turnstile entirely):
- Add frame-src for challenges.cloudflare.com. Without it the widget's
  iframe fell back to default-src 'self' and was blocked outright.
- Allow 'unsafe-eval' and websockets in DEVELOPMENT only. `next dev`
  compiles with eval(), so the strict policy threw EvalError and killed
  hydration — no client JS ran at all, which also meant form submit
  handlers never fired. Production policy is unchanged and still strict.

Also included (concurrent work in the tree):
- Admin organizations pages and lib/admin/orgs.
- Episode moderation migration, SEO metadata (sitemap, robots, JSON-LD,
  OG/Twitter images, manifest), Umami analytics, not-found page.

Local dev database: docker-compose.dev.yml provisions Postgres 18 on port
5443 (5432-5442 are in use by other local projects).

Note: `npx tsc --noEmit` currently fails in app/(app)/team/page.tsx — an
`invitations` prop the component does not accept. This predates the commit
and will fail `next build` until fixed.

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

app/(marketing)/page.tsx

@@ -1,3 +1,4 @@
+import type { Metadata } from "next";
 import Link from "next/link";
 import {
   ArrowRight,
@@ -14,12 +15,32 @@ import {
 import { Button } from "@/components/ui/button";
 import { Badge } from "@/components/ui/badge";
 import { Card, CardContent } from "@/components/ui/card";
+import { JsonLd } from "@/components/seo/json-ld";
 import { PLAN_ORDER, PLANS } from "@/lib/billing/plans";
+import { graph, softwareApplicationSchema, webPageSchema } from "@/lib/schema";
+import { SITE_DESCRIPTION, SITE_TAGLINE, absoluteUrl } from "@/lib/seo";
 import { formatPrice } from "@/lib/utils";
 
+export const metadata: Metadata = {
+  // The homepage keeps the root layout's title/description (they are already
+  // written for it); it only needs an explicit self-referencing canonical.
+  alternates: { canonical: absoluteUrl("/") },
+};
+
 export default function LandingPage() {
   return (
     <>
+      <JsonLd
+        data={graph(
+          webPageSchema({
+            path: "/",
+            name: SITE_TAGLINE,
+            description: SITE_DESCRIPTION,
+          }),
+          softwareApplicationSchema()
+        )}
+      />
+
       {/* Hero */}
       <section className="relative overflow-hidden bg-hero-wash">
         <div className="container flex flex-col items-center gap-7 py-24 text-center md:py-36">