Switch to Sustainable Use License (fair-code model)

- Replace ISC license with Sustainable Use License v1.0
- Add LICENSE_FAQ.md explaining the fair-code approach
- Update package.json with new license identifier
- Add license headers to main entry point files
- Update README with clear license usage guidelines

Following n8n's licensing approach, this provides:
- Free use for internal business purposes
- Free use for personal/non-commercial projects
- Restrictions on hosting as a service
- Protection against commercial exploitation

No .ee. mechanism implemented yet - all features remain
freely available under the single license.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

package.json

@@ -25,7 +25,7 @@
   },
   "keywords": [],
   "author": "",
-  "license": "ISC",
+  "license": "Sustainable-Use-1.0",
   "bugs": {
     "url": "https://github.com/czlonkowski/n8n-mcp/issues"
   },