security: fix full audit findings (v0.32.0)

Full list of the audit's confirmed findings and their fixes:

- Stored XSS via unescaped JSON-LD on the public recipe page
  (app/r/[id]/page.tsx) — escape < before injecting.
- CSP allowed unsafe-eval in production — now dev-only (Next prod
  never eval()s; only its HMR does).
- avatarUrl accepted any URL with no ownership check — now takes an
  avatarKey issued by avatar-presign, validated server-side, same
  pattern as recipe/review photos.
- No session revocation on password change/reset — both now revoke
  other sessions (revokeOtherSessions: true, revokeSessionsOnPasswordReset).
- Rate-limit bypass via spoofable X-Forwarded-For — take the last
  (proxy-appended) hop instead of the first (client-supplied) one,
  matching the single-Traefik-hop topology.
- Webhook signing secrets stored plaintext — now AES-256-GCM
  encrypted like every other secret in this app, with a legacy-
  plaintext fallback for pre-existing rows (bare hex has no ":", our
  ciphertext format always does).
- Better Auth's own rate limiter defaulted to in-memory storage,
  ineffective across replicas — now backed by the same Redis as
  lib/rate-limit.ts (secondaryStorage), with storeSessionInDatabase
  explicit so session storage itself doesn't move as a side effect.
- Presigned upload URLs didn't bind the declared file size to the
  actual upload, letting a client under-declare size (and quota
  charge) then PUT an arbitrarily large object — switched to S3
  presigned POST with a signed content-length-range condition,
  enforced by the storage server itself.
- generateMetadata() on the recipe page skipped the visibility
  filter the page body uses, leaking a private recipe's title via
  <title> to any signed-in user with the id.
- Block/unblock had no rate limit, unlike follow/unfollow.
- AI quota was charged even when a user's own BYOK key was used
  (their own credentials/billing) — added an isByok flag through
  the config-resolution chain and skip the charge when set. Also
  wired BYOK into generate/generate-from-idea/translate/import-url,
  which never looked it up at all before.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/next.config.ts

@@ -4,6 +4,13 @@ const storagePublicUrl = process.env["STORAGE_PUBLIC_URL"] || "http://localhost:
 const storageUrl = new URL(storagePublicUrl);
 const storageOrigin = storageUrl.origin;
 
+// unsafe-eval is only needed by Next.js dev's HMR/Fast Refresh — production
+// builds never eval(), so drop it there instead of leaving XSS payloads a
+// wide-open eval sink in the deployed app.
+const scriptSrc = process.env.NODE_ENV === "production"
+  ? "script-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net"
+  : "script-src 'self' 'unsafe-inline' 'unsafe-eval' https://cdn.jsdelivr.net";
+
 const securityHeaders = [
   {
     key: "X-Content-Type-Options",
@@ -33,7 +40,7 @@ const securityHeaders = [
     key: "Content-Security-Policy",
     value: [
       "default-src 'self'",
-      "script-src 'self' 'unsafe-inline' 'unsafe-eval' https://cdn.jsdelivr.net", // unsafe-eval needed by Next.js dev; tighten in prod. jsdelivr serves the Scalar API-reference bundle on /docs.
+      scriptSrc, // jsdelivr serves the Scalar API-reference bundle on /docs.
       "style-src 'self' 'unsafe-inline' https://cdn.jsdelivr.net",
       `img-src 'self' data: blob: ${storageOrigin} https://www.gravatar.com`,
       "font-src 'self' https://cdn.jsdelivr.net data:",