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/public/episodes/[shareId]/audio/route.ts

@@ -37,7 +37,9 @@ export async function GET(
   const { shareId } = await params;
 
   const episode = await prisma.episode.findUnique({
-    where: { shareId },
+    // A removed episode must be unreachable even if a share link is still
+    // circulating; moderatedAt is the takedown marker.
+    where: { shareId, moderatedAt: null },
     select: { audioAsset: { select: { storageKey: true } } },
   });
   const key = episode?.audioAsset?.storageKey;

app/api/public/episodes/[shareId]/cover/route.ts

@@ -42,7 +42,9 @@ export async function GET(
   const { shareId } = await params;
 
   const episode = await prisma.episode.findUnique({
-    where: { shareId },
+    // A removed episode must be unreachable even if a share link is still
+    // circulating; moderatedAt is the takedown marker.
+    where: { shareId, moderatedAt: null },
     select: { coverArt: { select: { storageKey: true } } },
   });
   const key = episode?.coverArt?.storageKey;