feat(push): native device-token registration + FCM/APNs senders

- /api/v1/devices (register) + /api/v1/devices/remove — auth-required, validates
  platform (ios|android), upserts by token; e2e covers register/validation/auth/remove.
- db device_tokens table + deviceTokens repo.
- push.js: FCM HTTP v1 (Android) and APNs token-based over HTTP/2 (iOS) folded into
  the single push.sendToUser path alongside Web Push; each transport independently
  config-gated and a silent no-op without creds. Dead tokens pruned on 404/410.
- docs: CLIENTS.md Phase B updated; DEPLOY.md env table adds FCM/APNs vars.

e2e 117/117.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/db.js

@@ -306,6 +306,21 @@ CREATE TABLE IF NOT EXISTS push_subscriptions (
 CREATE INDEX IF NOT EXISTS idx_push_user ON push_subscriptions(user_id);
 `);
 
+// Native device push tokens (FCM for Android, APNs for iOS) registered by the mobile app.
+// Distinct from push_subscriptions (Web Push): a native token is just an opaque string + platform.
+db.exec(`
+CREATE TABLE IF NOT EXISTS device_tokens (
+  id TEXT PRIMARY KEY,
+  user_id TEXT NOT NULL,
+  tenant_id TEXT,
+  platform TEXT NOT NULL,
+  token TEXT NOT NULL UNIQUE,
+  created_at INTEGER NOT NULL,
+  last_seen INTEGER
+);
+CREATE INDEX IF NOT EXISTS idx_devtok_user ON device_tokens(user_id);
+`);
+
 // Favourite conversations (per user). target = 'dm:<userId>' or 'group:<groupId>'.
 db.exec(`
 CREATE TABLE IF NOT EXISTS favorites (