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/index.js

@@ -264,6 +264,15 @@ if (RECAP_MODE === "multi") {
   // public URL + relay being configured, so it's a safe no-op until then.
   const { startReminderScheduler } = await import("./subscription-reminders.js");
   startReminderScheduler();
+  // Daily Digest: opt-in (off by default) once-a-day email of a user's
+  // last ~24h of library recaps. Same self-gating shape as reminders —
+  // no-op until SMTP + public URL are set. The one-click unsubscribe GET
+  // is public (whitelisted in tenant-auth) since the email has no session.
+  const { startDigestScheduler, setupDigestRoutes } = await import(
+    "./daily-digest.js"
+  );
+  setupDigestRoutes(app);
+  startDigestScheduler();
 
   // /api/account/whoami — frontend hits this on every page load to
   // determine which UI state to render: