docs(#23): install guide, admin guide, reseller guide, user guide, API reference

Five markdown documents covering the full panel:
- docs/README.md: index with links to all guides
- docs/install.md: requirements, one-liner install, file layout, config.ini, auto-deploy, upgrade
- docs/admin-guide.md: all admin panel sections (accounts, DNS, mail, security, Docker, notifications, WHMCS)
- docs/reseller-guide.md: account management, white-label branding, Docker quotas
- docs/user-guide.md: files, email, databases, FTP, DNS, SSL, cron, Docker, settings
- docs/api-reference.md: all 25+ endpoints with request/response shapes, auth, rate limits, role access

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/README.md

@@ -0,0 +1,24 @@
+# NovaCPX Documentation
+
+NovaCPX is an open-source Linux web hosting control panel with three-tier management (Admin → Reseller → User).
+
+## Documents
+
+| Guide | Audience | Description |
+|-------|----------|-------------|
+| [Installation Guide](install.md) | Server admins | Requirements, installer usage, file layout, auto-deploy setup |
+| [Admin Guide](admin-guide.md) | Server admins | All admin panel features: accounts, DNS, mail, security, Docker, notifications |
+| [Reseller Guide](reseller-guide.md) | Resellers | Creating and managing customer accounts, white-label branding |
+| [User Guide](user-guide.md) | End users | Files, email, databases, FTP, DNS, SSL, cron, Docker |
+| [API Reference](api-reference.md) | Developers | Full REST API documentation for all endpoints |
+
+## Quick links
+
+- Admin panel: `https://<server>:8882`
+- Reseller panel: `https://<server>:8881`
+- User panel: `https://<server>:8880`
+- Webmail: `https://<server>:8883`
+
+## Source
+
+GitHub: [myronblair/novacpx](https://github.com/myronblair/novacpx)