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.

startos/versions/v0.2.158.ts

@@ -0,0 +1,13 @@
+import { VersionInfo } from '@start9labs/start-sdk'
+
+export const v_0_2_158 = VersionInfo.of({
+  version: '0.2.158:0',
+  releaseNotes: {
+    en_US:
+      'New: opt-in Daily Digest — a once-a-day email summarizing the recaps you added to your library in the last 24 hours, each as a short synthesized overview. Off by default; turn it on in Settings, and every email has a one-click unsubscribe.',
+  },
+  migrations: {
+    up: async ({ effects }) => {},
+    down: async ({ effects }) => {},
+  },
+})