Add chat support

Here is the updated Agile Story, refined for a **library-first** architecture. This version ensures the core logic remains independent of any specific UI, allowing you to link it to your Qt trading terminal, a CLI tool, or even an automated LLM service.

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## **User Story: Modular Binary Chat Library & Event System**

### **1. High-Level Summary**

**As a** system architect,

**I want** to develop a standalone C++ "Chat & Event Engine" library

**So that** real-time communication, system notifications, and LLM interactions
can be shared across our Qt GUI, headless CLI tools, and backend services using
our existing binary protocol.

### **2. Architectural Foundation (The "Engine")**

- **Library Type:** A "headless" C++ shared/static library (`libtradingchat`)
  with **no UI dependencies**.
- **Transport:** **Boost.Asio** for asynchronous TCP/TLS networking.
- **Message Broker:** PostgreSQL **`LISTEN/NOTIFY`** for cross-instance message
  distribution.
- **Concurrency:** The library manages its own `boost::asio::io_context` in a
  background thread to ensure networking never blocks the consumer's UI thread.

### **3. Core Identity & Payload Design**

- **Universal Identity:** Support for three `UserTypes`: `Human`, `System`, and `LLM`.
- **Flexible Payloads:**
- `CHAT_MSG`: Standard binary-serialized text.
- `SYSTEM_ALERT`: High-priority event notifications.
- `RICH_DATA`: Raw binary blobs for charts, order book snapshots, etc.

- **The "Observer" Interface:** The library will use a **Callback API** (via
  `std::function` or an abstract `IChatObserver` class) to notify consumers of
  events like `onMessage`, `onStatusChange`, and `onHistoryLoaded`.

### **4. Technical Tasks for Implementation**

#### **A. Database & Backend (Postgres)**

- Create a schema that stores messages in a `BYTEA` column to preserve your
  bespoke binary format.
- Implement a trigger that notifies a channel based on `RoomID`.

#### **B. Core Library (Plain C++17/20)**

- **Protocol Parser:** Logic to wrap/unwrap your bespoke binary headers.
- **The Manager:** A `ChatClient` class that handles the connection lifecycle.
- **Notification Listener:** A dedicated Postgres connection using `libpqxx` to
  monitor the `LISTEN` stream.
- **History Fetcher:** Logic to request and deserialize "scroll-back" messages
  from Postgres.

#### **C. Consumers (The Frontends)**

- **Qt Bridge:** A `QObject` wrapper that consumes the library's callbacks and
  emits Qt Signals (to be handled by QML or Widgets).
- **CLI Tool:** A lightweight consumer that prints incoming binary data to
  `stdout` for debugging and automated monitoring.

### **5. Acceptance Criteria**

- [ ] **Modular Testing:** The core library can be compiled and tested using a
  CLI-only test runner (no Qt required).
- [ ] **Binary Integrity:** Bespoke binary packets remain bit-perfect from the
  sender, through the Postgres `BYTEA` storage, to the receiver.
- [ ] **Thread Safety:** Messages received on the Boost.Asio thread are safely dispatched to the consumer via callbacks.
- [ ] **LLM Integration:** An LLM service can consume this library to "listen"
  and "reply" as a Type 2 user.