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/api/episodes/[id]/export/route.ts

@@ -3,6 +3,7 @@ import JSZip from "jszip";
 import { getServerSession } from "@/lib/auth/guards";
 import { prisma } from "@/lib/db";
 import { storage } from "@/lib/storage";
+import { rateLimit, LIMITS } from "@/lib/ratelimit";
 import type { StructuredScript } from "@/lib/ai/types";
 
 export const dynamic = "force-dynamic";
@@ -25,6 +26,16 @@ export async function GET(
   const session = await getServerSession();
   if (!session) return new Response("Unauthorized", { status: 401 });
 
+  // This handler buffers the full MP3 + cover into a JSZip in memory, so an
+  // authenticated user looping it is a cheap way to exhaust the heap.
+  const rl = await rateLimit("export", session.user.id, LIMITS.export);
+  if (!rl.ok) {
+    return new Response("Too many exports. Please slow down.", {
+      status: 429,
+      headers: { "Retry-After": String(rl.retryAfterSec ?? 60) },
+    });
+  }
+
   const episode = await prisma.episode.findUnique({
     where: { id },
     include: {
@@ -38,6 +49,11 @@ export async function GET(
   if (episode.userId !== session.user.id && session.user.role !== "admin") {
     return new Response("Forbidden", { status: 403 });
   }
+  // Removed content stays downloadable for admins (evidence/appeals) but not
+  // for the owner, who would otherwise just re-publish it elsewhere.
+  if (episode.moderatedAt && session.user.role !== "admin") {
+    return new Response("This episode was removed for a policy violation.", { status: 451 });
+  }
 
   const speakerNames: Record<string, string> = {};
   for (const s of episode.speakers) speakerNames[s.speakerKey] = s.displayName;