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/history.js

@@ -220,6 +220,43 @@ export async function loadSession(scope, id) {
   }
 }
 
+// List a scope's saved sessions as lightweight metadata (no entries /
+// chunks), oldest first. The daily-digest scan uses this to pick recaps
+// created after a watermark before loading each full record for
+// synthesis. Returns [] when the scope has no library yet (or the id is
+// malformed — safeComponent throws inside scopeDir, caught here).
+export async function listScopeSessions(scope) {
+  let dir;
+  try {
+    dir = scopeDir(scope);
+  } catch {
+    return [];
+  }
+  let files = [];
+  try {
+    files = await fs.readdir(dir);
+  } catch {
+    return [];
+  }
+  const out = [];
+  for (const file of files.filter(
+    (f) => f.endsWith(".json") && !f.startsWith("_") && !ROOT_SIDECARS.has(f),
+  )) {
+    try {
+      const data = JSON.parse(await fs.readFile(path.join(dir, file), "utf-8"));
+      out.push({
+        id: data.id,
+        title: data.title,
+        type: data.type || "youtube",
+        url: data.url,
+        createdAt: data.createdAt,
+      });
+    } catch {}
+  }
+  out.sort((a, b) => new Date(a.createdAt) - new Date(b.createdAt));
+  return out;
+}
+
 // Shallow-merge `patch` into a session record on disk (e.g. to stamp
 // `summaryAudio` availability). No-op-safe: returns null if the record
 // is missing rather than throwing.