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>

next.config.mjs

@@ -16,6 +16,23 @@ const nextConfig = {
       { protocol: "https", hostname: "images.unsplash.com" },
     ],
   },
+  // Serve the self-hosted Umami tracker and its /api/send beacon from this
+  // origin. The CSP in middleware.ts uses 'strict-dynamic', which makes browsers
+  // ignore host allowlists in script-src, and connect-src is 'self' — so a
+  // third-party tracker could not be allowlisted without weakening the policy.
+  // Proxying keeps both same-origin, and content blockers leave it alone.
+  async rewrites() {
+    const host = process.env.UMAMI_HOST_URL?.trim().replace(/\/+$/, "");
+    if (!host) return [];
+    return [{ source: "/_a/:path*", destination: `${host}/:path*` }];
+  },
+  // The OG image route reads the brand mark off disk. That path is built at
+  // runtime so Next's static file tracing cannot infer it — list it explicitly so
+  // the asset is copied into the standalone output as well.
+  outputFileTracingIncludes: {
+    "/opengraph-image": ["./app/icon.png"],
+    "/twitter-image": ["./app/icon.png"],
+  },
   // Server-only packages that should be required at runtime, not bundled by webpack.
   // better-auth ships internal adapters (kysely) that break webpack's ESM analysis.
   serverExternalPackages: ["pg-boss", "@prisma/client", "better-auth"],