docs: add Bybit, OKX, and Lighter exchange support

- Mark Bybit, OKX as supported in CEX section
- Mark Lighter as supported in Perp-DEX section
- Add Bybit API setup guide
- Add OKX API setup guide
- Add Lighter agent wallet setup guide
- Update all READMEs (EN, ZH-CN, JA, KO)

docs/getting-started/okx-api.md

@@ -0,0 +1,75 @@
+# OKX API Setup Guide
+
+This guide explains how to create and configure OKX API keys for use with NOFX.
+
+## Create API Key
+
+1. Log in to your [OKX account](https://www.okx.com/join/1865360)
+2. Go to **Account** → **API**
+3. Click **Create API Key**
+4. Select **Trade** as the purpose
+5. Complete 2FA verification
+6. Name your API key (e.g., "NOFX Trading")
+
+## Configure API Permissions
+
+Enable the following permissions:
+
+- ✅ **Read** - Required
+- ✅ **Trade** - Required for trading
+- ❌ **Withdraw** - Keep disabled for security
+
+## Passphrase
+
+OKX requires a passphrase in addition to API Key and Secret:
+
+1. Create a strong passphrase during API creation
+2. Save it securely - you'll need it for configuration
+
+## IP Whitelist (Recommended)
+
+For enhanced security:
+
+1. Click **Edit** on your API key
+2. Enable **IP Whitelist**
+3. Add your server's IP address
+4. Save changes
+
+## Save Your Keys
+
+After creation, you'll have:
+- **API Key**: `xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`
+- **Secret Key**: `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx`
+- **Passphrase**: Your created passphrase
+
+⚠️ **Important**: Save the Secret Key immediately - it's only shown once!
+
+## Configure in NOFX
+
+Add your API credentials through the NOFX web interface:
+
+1. Open NOFX dashboard (http://localhost:3000)
+2. Go to **Exchange Configuration**
+3. Enable **OKX**
+4. Enter:
+   - **API Key**
+   - **Secret Key**
+   - **Passphrase**
+5. Save configuration
+
+## Troubleshooting
+
+| Error | Solution |
+|-------|----------|
+| `Invalid API key` | Check if API key is correct |
+| `Invalid signature` | Check if Secret key and Passphrase are correct |
+| `IP not whitelisted` | Add your IP to whitelist or disable IP restriction |
+| `Permission denied` | Enable Trade permission in API settings |
+
+## Security Best Practices
+
+- Never share your API keys or passphrase
+- Use IP whitelisting
+- Don't enable withdrawal permissions
+- Create separate API keys for different applications
+- Regularly rotate your API keys