docs: implement professional documentation structure and project hygiene

docs/architecture.md

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+# Architecture Overview
+
+Plexus is designed as a real-time, decentralized-first chat application.
+
+## 🏗 System Components
+
+### 1. Frontend (Client)
+- Built with **Vue 3** and **Vite**.
+- Uses **Pinia** for state management (messages, users, channels).
+- Communicates with the backend via **Socket.IO** for real-time updates.
+- Simulates Solana transactions for messages, reactions, and username changes.
+
+### 2. Backend (Server)
+- Built with **Node.js** and **Express**.
+- Uses **Socket.IO** to handle real-time communication.
+- **DuckDB** is used as the primary data store for:
+    - User profiles (wallet addresses, unique usernames).
+    - Message history.
+    - Reactions.
+
+### 3. Database Schema
+- `users`: `wallet_address` (PK), `username` (UNIQUE), `last_seen`.
+- `messages`: `id` (PK), `channel_id`, `wallet_address`, `content`, `timestamp`, `tx_id`.
+- `reactions`: `message_id`, `wallet_address`, `emoji`.
+
+## 🔄 Data Flow
+
+1. **User Joins**: Client emits `join` with wallet address and requested username. Server verifies/generates unique username and updates `users` table.
+2. **Sending Message**: Client simulates transaction, then emits `sendMessage` with `txId`. Server saves message to DuckDB and broadcasts `newMessage` to all clients.
+3. **Reactions**: Client emits `toggleReaction`. Server updates `reactions` table and broadcasts `updateReactions`.
+
+## 🛡 Security
+- Currently uses a simple wallet-based identification.
+- Future versions will implement full message signing and verification.