Send app broadcasts as Resend Broadcasts; add selective import from Resend; v2.7.0

- Broadcast Email creates and sends a Resend Broadcast to the Resend segment (unsubscribe handling, reports, New Episode topic, scheduling, test send)
- Subscribers: import chosen Resend-only contacts into the app list

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/App.css

@@ -12989,3 +12989,6 @@
 .cmp-rows li { display: flex; flex-wrap: wrap; gap: 0.2rem 1rem; padding: 0.25rem 0; border-bottom: 1px solid rgba(255, 255, 255, 0.05); overflow-wrap: anywhere; }
 .cmp-rows li span { min-width: 140px; opacity: 0.85; }
 .cmp-more { opacity: 0.6; }
+.cmp-rows li input[type="checkbox"] { flex-shrink: 0; margin-top: 0.15rem; }
+.cmp-selectall { opacity: 0.85; font-weight: 600; }
+.cmp-selectall label { display: inline-flex; gap: 0.4rem; align-items: center; cursor: pointer; }