Dual Platform Chat Reply System -- 2

I want a straightforward chat-reply service that lives both on the web and inside a mobile app. Its single, non-negotiable feature today is automatic messaging: when someone writes to me, an auto-response must go out instantly so no inquiry is ever left hanging.

On the web side, a clean responsive interface is enough—conversation list, message window, and a small settings screen where I can create, edit, enable, or disable canned replies. The mobile app (Android and iOS or any reliable cross-platform approach) should mirror that same flow and stay perfectly in sync with the browser version through a shared API backend.

Deliverables
• Responsive web client built with any modern framework you prefer.
• Native or cross-platform mobile app delivering identical functionality.
• Unified backend and database that both clients consume.
• Admin panel for managing auto-messages and basic trigger rules (keywords, time-of-day, etc.).
• Clear deployment instructions so I can host everything myself.

Acceptance criteria
1. A new incoming message triggers my predefined reply within two seconds.
2. Edits made on one platform reflect immediately on the other.
3. Source code is delivered in a Git repository with a concise README.

Right now I only need the auto-reply feature, but please architect the code cleanly so future add-ons like CRM hooks or real-time analytics can slot in without major rewrites.