feat: landing page + logo, dev-mode banner + sync cap, non-blocking sync with progress splash

docker-compose.yml

@@ -27,6 +27,10 @@ services:
       GoogleOAuth__ClientId: ${GOOGLE_CLIENT_ID:-}
       GoogleOAuth__ClientSecret: ${GOOGLE_CLIENT_SECRET:-}
       Ai__Mode: ${AI_MODE:-Disabled}
+      # Dev mode shows the dev banner and caps the initial sync. Set DEV_MODE=true
+      # and MAX_MESSAGES=1000 in deploy/.env to exercise it in this Docker setup.
+      App__DevMode: ${DEV_MODE:-false}
+      GmailSync__MaxMessages: ${MAX_MESSAGES:-0}
       Cors__Origins__0: ${FRONTEND_ORIGIN:-http://localhost:8081}
     volumes:
       - keys:/keys