Sponsor to downline messaging: lineage view, daily broadcast (email+inbox), login modal

- Downline resolver (3 levels); email visible for directs only, username+ID deeper
- Broadcast composer (rich editor) to directs or full downline, 1/day cap, sends email + on-site inbox
- Upline messages inbox in My line; unmissable sign-in modal for unread, ack marks read
- messages.js dual-mode store; sponsor_messages table; sanitizeRich reused

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

db.js

@@ -110,6 +110,17 @@ async function bootstrap() {
   await alterSafe('ALTER TABLE campaigns ADD COLUMN height INT NULL');  // banner size (IAB) → also NAS height
   await alterSafe('ALTER TABLE campaigns ADD COLUMN nas_ad_id INT NULL');          // syndicated NAS sponsorads.ID
   await alterSafe('ALTER TABLE campaigns ADD COLUMN nas_served INT NOT NULL DEFAULT 0'); // NAS impressions already reconciled into spend
+  await q(`CREATE TABLE IF NOT EXISTS sponsor_messages (
+    id INT AUTO_INCREMENT PRIMARY KEY,
+    from_member INT NOT NULL,
+    from_email VARCHAR(190) NOT NULL,
+    to_email VARCHAR(190) NOT NULL,
+    subject VARCHAR(160) NOT NULL,
+    body TEXT NULL,
+    sent BIGINT NOT NULL,
+    read_ts BIGINT NULL,
+    INDEX (to_email, read_ts), INDEX (from_email, sent)
+  ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4`);
   await q(`CREATE TABLE IF NOT EXISTS burns (
     id VARCHAR(32) PRIMARY KEY,
     member_id INT NOT NULL,