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.

public/index.html

@@ -2362,6 +2362,9 @@
       // User's own active sessions (lite-settings tenant view). Loaded
       // on demand when the Settings modal opens.
       mySessions: { rows: null, loading: false, error: null },
+      // Daily Digest opt-in (lite-settings tenant view). enabled is null
+      // until loaded from /api/account/digest when the modal opens.
+      digest: { enabled: null, loading: false, saving: false },
       // "Take Recap home" — fetches the tenant's raw license key on
       // demand. We don't load this in /api/account/whoami because the
       // key is a bearer credential we'd rather not pass through the
@@ -7343,6 +7346,7 @@
                 ${state.account?.user ? renderClaimPurchaseBlock() : ""}
                 ${state.account?.user ? renderPasswordBlock() : ""}
                 ${state.account?.user ? renderMySessionsBlock() : ""}
+                ${state.account?.user ? renderDigestBlock() : ""}
                 ${renderLibraryTransfer()}
                 ${state.account?.user ? renderTenantDangerZone() : ""}
               </div>
@@ -7874,6 +7878,33 @@
       `;
     }
 
+    // Daily Digest opt-in toggle. Off by default; a single switch that
+    // POSTs /api/account/digest. enabled is null until loaded — show a
+    // muted "Loading…" rather than a misleading unchecked box during the
+    // round-trip so the user never sees the wrong initial state.
+    function renderDigestBlock() {
+      const d = state.digest || {};
+      const checkboxAttrs =
+        d.enabled === null || d.loading || d.saving ? "disabled" : "";
+      return `
+        <label class="field-label" style="margin-top:14px;">Daily digest</label>
+        <div style="border:1px solid #1e293b;background:rgba(15,23,42,0.4);border-radius:8px;padding:12px;">
+          <label style="display:flex;align-items:flex-start;gap:8px;font-size:12px;color:#cbd5e1;cursor:${checkboxAttrs ? "default" : "pointer"};">
+            <input type="checkbox" ${d.enabled ? "checked" : ""} ${checkboxAttrs}
+              onchange="setDigestEnabled(this.checked)" style="margin:2px 0 0;" />
+            <span>
+              Email me a daily digest
+              <span style="color:#64748b;display:block;font-size:10px;margin-top:2px;line-height:1.5;">
+                ${d.enabled === null
+                  ? "Loading…"
+                  : "A once-a-day email summarizing the recaps you added to your library in the last 24 hours. Off by default; skipped on days with nothing new."}
+              </span>
+            </span>
+          </label>
+        </div>
+      `;
+    }
+
     // Danger Zone — sits at the very bottom of the tenant lite-settings
     // modal. One action for now (Delete Account); future destructive
     // self-actions land here. Visually muted by default to avoid being
@@ -10264,6 +10295,7 @@
           loadAdminActivity(state.ops.activityHours || 24);
         } else if (state.account?.user) {
           loadMySessions();
+          loadMyDigest();
         }
       }
       render();
@@ -12012,6 +12044,46 @@
       }
     }
 
+    async function loadMyDigest() {
+      state.digest.loading = true;
+      render();
+      try {
+        const res = await fetch(`${API_BASE}/api/account/digest`);
+        if (!res.ok) throw new Error(`HTTP ${res.status}`);
+        const data = await res.json();
+        state.digest.enabled = !!data.enabled;
+      } catch (e) {
+        // Leave enabled null; the block keeps showing "Loading…" rather
+        // than asserting a state we couldn't confirm.
+      } finally {
+        state.digest.loading = false;
+        render();
+      }
+    }
+
+    async function setDigestEnabled(enabled) {
+      const prev = state.digest.enabled;
+      // Optimistic flip so the switch responds instantly; revert on error.
+      state.digest.enabled = enabled;
+      state.digest.saving = true;
+      render();
+      try {
+        const res = await fetch(`${API_BASE}/api/account/digest`, {
+          method: "POST",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({ enabled }),
+        });
+        if (!res.ok) throw new Error(`HTTP ${res.status}`);
+        showToast(enabled ? "Daily digest on" : "Daily digest off", "✓");
+      } catch (e) {
+        state.digest.enabled = prev;
+        showToast("Couldn't save that — try again", "!");
+      } finally {
+        state.digest.saving = false;
+        render();
+      }
+    }
+
     async function revokeMySession(sessionId) {
       try {
         const res = await fetch(