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/assets/[...key]/route.ts

@@ -33,15 +33,25 @@ export async function GET(
 
   // Resolve the owning episode from the asset record so we can authorize.
   const [audio, art] = await Promise.all([
-    prisma.audioAsset.findFirst({ where: { storageKey: key }, select: { episode: { select: { userId: true } } } }),
-    prisma.coverArt.findFirst({ where: { storageKey: key }, select: { episode: { select: { userId: true } } } }),
+    prisma.audioAsset.findFirst({
+      where: { storageKey: key },
+      select: { episode: { select: { userId: true, moderatedAt: true } } },
+    }),
+    prisma.coverArt.findFirst({
+      where: { storageKey: key },
+      select: { episode: { select: { userId: true, moderatedAt: true } } },
+    }),
   ]);
-  const ownerId = audio?.episode.userId ?? art?.episode.userId;
-  if (!ownerId) return new Response("Not found", { status: 404 });
+  const owningEpisode = audio?.episode ?? art?.episode;
+  if (!owningEpisode) return new Response("Not found", { status: 404 });
 
-  const isOwner = ownerId === session.user.id;
+  const isOwner = owningEpisode.userId === session.user.id;
   const isAdmin = session.user.role === "admin";
   if (!isOwner && !isAdmin) return new Response("Forbidden", { status: 403 });
+  // Admins keep access to removed media for appeals; the owner does not.
+  if (owningEpisode.moderatedAt && !isAdmin) {
+    return new Response("This episode was removed for a policy violation.", { status: 451 });
+  }
 
   // Stream off disk instead of buffering the whole file into memory.
   const total = await storage().size(key);