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/sitemap.ts

@@ -0,0 +1,40 @@
+import type { MetadataRoute } from "next";
+import { absoluteUrl } from "@/lib/seo";
+
+/**
+ * /sitemap.xml — the public, indexable surface only.
+ *
+ * Authed routes, auth screens and unlisted /p/<shareId> share pages are
+ * deliberately absent: they are `noindex` and disallowed in robots.ts, and a
+ * sitemap that lists non-indexable URLs is a Search Console error.
+ */
+
+/** Legal pages change rarely; keep their stamp tied to the published revision. */
+const LEGAL_UPDATED = new Date("2026-06-07T00:00:00.000Z");
+
+type Entry = {
+  path: string;
+  priority: number;
+  changeFrequency: MetadataRoute.Sitemap[number]["changeFrequency"];
+  lastModified: Date;
+};
+
+const NOW = new Date();
+
+const ROUTES: Entry[] = [
+  { path: "/", priority: 1.0, changeFrequency: "weekly", lastModified: NOW },
+  { path: "/features", priority: 0.9, changeFrequency: "monthly", lastModified: NOW },
+  { path: "/pricing", priority: 0.9, changeFrequency: "monthly", lastModified: NOW },
+  { path: "/faq", priority: 0.8, changeFrequency: "monthly", lastModified: NOW },
+  { path: "/about", priority: 0.6, changeFrequency: "yearly", lastModified: NOW },
+  { path: "/terms", priority: 0.3, changeFrequency: "yearly", lastModified: LEGAL_UPDATED },
+  { path: "/privacy", priority: 0.3, changeFrequency: "yearly", lastModified: LEGAL_UPDATED },
+  { path: "/cookies", priority: 0.3, changeFrequency: "yearly", lastModified: LEGAL_UPDATED },
+  { path: "/acceptable-use", priority: 0.3, changeFrequency: "yearly", lastModified: LEGAL_UPDATED },
+  { path: "/refunds", priority: 0.3, changeFrequency: "yearly", lastModified: LEGAL_UPDATED },
+  { path: "/subprocessors", priority: 0.3, changeFrequency: "yearly", lastModified: LEGAL_UPDATED },
+];
+
+export default function sitemap(): MetadataRoute.Sitemap {
+  return ROUTES.map(({ path, ...rest }) => ({ url: absoluteUrl(path), ...rest }));
+}