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/(app)/series/actions.ts

@@ -13,6 +13,7 @@ import type { UsageMetric } from "@/lib/billing/plans";
 import { FORMAT_SPEAKERS } from "@/lib/episodes/options";
 import { DEFAULT_VOICE_IDS, VOICE_CATALOG } from "@/lib/ai/voices";
 import { isFlagEnabled } from "@/lib/flags";
+import { rateLimit, LIMITS } from "@/lib/ratelimit";
 
 const createSchema = z.object({
   theme: z.string().min(5).max(500),
@@ -30,6 +31,16 @@ export async function createSeriesAction(
   if (!(await subjectHasFeature(session.user.id, "series_generator", session.session.activeOrganizationId))) {
     return { ok: false, error: "The series generator requires the Pro plan." };
   }
+
+  // planSeason() below is an uncapped GPT-4o completion that is NOT metered
+  // against a monthly quota (unlike script/audio/art), so the rate limit is the
+  // only thing bounding AI spend here. Keep it tight — a season plan is a rare,
+  // deliberate action, so an hourly bucket is the right shape.
+  const rl = await rateLimit("series-plan", session.user.id, LIMITS.seriesPlan);
+  if (!rl.ok) {
+    return { ok: false, error: `Too many series plans. Try again in ${Math.ceil(rl.retryAfterSec! / 60)}m.` };
+  }
+
   if (!(await isFlagEnabled("episode_generation_enabled"))) {
     return { ok: false, error: "Generation is temporarily paused. Please try again shortly." };
   }
@@ -60,6 +71,11 @@ export async function generateFromSeriesAction(
   const session = await getServerSession();
   if (!session) return { ok: false, error: "You must be signed in." };
 
+  const rl = await rateLimit("generation", session.user.id, LIMITS.generation);
+  if (!rl.ok) {
+    return { ok: false, error: `Too many requests. Try again in ${rl.retryAfterSec}s.` };
+  }
+
   if (!(await isFlagEnabled("episode_generation_enabled"))) {
     return { ok: false, error: "Episode generation is temporarily paused. Please try again shortly." };
   }