chore: switch to AGPLv3 dual-license

Replace MIT with AGPLv3 + commercial dual-license. Add copyright header
and dual-license notice to LICENSE, add CLA to CONTRIBUTING.md, update
README license section, and update all package.json license fields.

apps/docs/package.json

@@ -10,5 +10,6 @@
   "devDependencies": {
     "tsx": "^4.19.0",
     "vitepress": "^1.1.4"
-  }
+  },
+  "license": "AGPL-3.0"
 }