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>

components/auth/turnstile.tsx

@@ -0,0 +1,146 @@
+"use client";
+
+import { forwardRef, useEffect, useImperativeHandle, useRef } from "react";
+
+const SCRIPT_ID = "cf-turnstile-script";
+const SCRIPT_SRC = "https://challenges.cloudflare.com/turnstile/v0/api.js?render=explicit";
+
+type TurnstileApi = {
+  render: (el: HTMLElement, opts: Record<string, unknown>) => string;
+  reset: (id: string) => void;
+  remove: (id: string) => void;
+};
+
+declare global {
+  // eslint-disable-next-line no-var
+  var turnstile: TurnstileApi | undefined;
+}
+
+/**
+ * Load Cloudflare's script once per page, no matter how many widgets mount.
+ * `render=explicit` keeps control in our hands so the widget can be reset —
+ * Turnstile tokens are single-use, so every failed submit needs a fresh one.
+ */
+let scriptPromise: Promise<void> | null = null;
+function loadTurnstileScript(): Promise<void> {
+  if (typeof window === "undefined") return Promise.resolve();
+  if (window.turnstile) return Promise.resolve();
+  if (scriptPromise) return scriptPromise;
+
+  scriptPromise = new Promise<void>((resolve, reject) => {
+    const existing = document.getElementById(SCRIPT_ID) as HTMLScriptElement | null;
+    if (existing) {
+      existing.addEventListener("load", () => resolve());
+      existing.addEventListener("error", () => reject(new Error("Turnstile failed to load")));
+      return;
+    }
+    const script = document.createElement("script");
+    script.id = SCRIPT_ID;
+    script.src = SCRIPT_SRC;
+    script.async = true;
+    script.defer = true;
+    script.onload = () => resolve();
+    script.onerror = () => {
+      // Allow a later mount to retry (e.g. the user was briefly offline).
+      scriptPromise = null;
+      reject(new Error("Turnstile failed to load"));
+    };
+    document.head.appendChild(script);
+  });
+  return scriptPromise;
+}
+
+/**
+ * `script.onload` does not guarantee `window.turnstile` is assigned yet, and the
+ * original code silently gave up forever when it wasn't — the widget would just
+ * never appear. Poll briefly instead so a slow parse still resolves.
+ */
+async function waitForTurnstileApi(timeoutMs = 10_000): Promise<void> {
+  const deadline = Date.now() + timeoutMs;
+  while (!window.turnstile && Date.now() < deadline) {
+    await new Promise((r) => setTimeout(r, 50));
+  }
+}
+
+export type TurnstileHandle = { reset: () => void };
+
+type TurnstileProps = {
+  siteKey: string;
+  /** Fires with the solved token, or "" whenever the token becomes unusable. */
+  onToken: (token: string) => void;
+  onError?: () => void;
+  className?: string;
+};
+
+/**
+ * Renders the Turnstile challenge. The parent owns the token and must send it
+ * as the `x-captcha-response` header; verification happens server-side in
+ * `lib/auth/auth.ts`.
+ */
+export const Turnstile = forwardRef<TurnstileHandle, TurnstileProps>(function Turnstile(
+  { siteKey, onToken, onError, className },
+  ref
+) {
+  const containerRef = useRef<HTMLDivElement>(null);
+  const widgetIdRef = useRef<string | null>(null);
+
+  // Hold the callbacks in refs so re-renders never tear down the widget —
+  // re-rendering it would drop a token the user already solved.
+  const onTokenRef = useRef(onToken);
+  const onErrorRef = useRef(onError);
+  onTokenRef.current = onToken;
+  onErrorRef.current = onError;
+
+  useImperativeHandle(
+    ref,
+    () => ({
+      reset() {
+        if (widgetIdRef.current && window.turnstile) {
+          window.turnstile.reset(widgetIdRef.current);
+          onTokenRef.current("");
+        }
+      },
+    }),
+    []
+  );
+
+  useEffect(() => {
+    let cancelled = false;
+
+    loadTurnstileScript()
+      .then(() => waitForTurnstileApi())
+      .then(() => {
+        if (cancelled || widgetIdRef.current || !containerRef.current || !window.turnstile) return;
+        widgetIdRef.current = window.turnstile.render(containerRef.current, {
+          sitekey: siteKey,
+          // The auth screens render outside next-themes' provider, so let the
+          // widget follow the OS colour scheme instead of the app's theme.
+          theme: "auto",
+          callback: (token: string) => onTokenRef.current(token),
+          // Any of these means we no longer hold a usable token.
+          "error-callback": () => {
+            onTokenRef.current("");
+            onErrorRef.current?.();
+          },
+          "expired-callback": () => onTokenRef.current(""),
+          "timeout-callback": () => onTokenRef.current(""),
+        });
+      })
+      .catch(() => onErrorRef.current?.());
+
+    return () => {
+      cancelled = true;
+      const id = widgetIdRef.current;
+      widgetIdRef.current = null;
+      if (id && window.turnstile) {
+        try {
+          window.turnstile.remove(id);
+        } catch {
+          // Widget already gone (e.g. React 18/19 StrictMode double-invoke).
+        }
+      }
+    };
+  }, [siteKey]);
+
+  return <div ref={containerRef} className={className} />;
+});