Add opt-in Daily Digest (daily email of last 24h of library recaps)

Multi-mode, off by default. Each new recap is synthesized into a 1-2
paragraph overview via the relay (operator-absorbed) and cached onto the
session JSON; a daily 08:00 scan emails opted-in users their fresh
recaps, deduped by a per-user watermark that never skips a failed or
over-cap recap. One-click tokenized unsubscribe; settings-modal toggle;
admin test trigger. Bumps to 0.2.158.

server/tenant-auth.js

@@ -35,6 +35,7 @@ const PUBLIC_PATH_PREFIXES = [
   "/api/health",
   "/api/auth/", // future client-facing auth shims (CSRF token issue, etc.)
   "/api/btcpay/webhook", // BTCPay needs to reach this without a session
+  "/api/digest/unsubscribe", // one-click unsubscribe from a digest email (no session)
   "/api/network-mode", // returns lan-vs-local; safe to expose
   "/api/relay/status", // public relay capabilities — pre-trial visibility
   "/api/account/whoami", // returns state — anonymous visitors must call this