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/api/package.json

@@ -47,5 +47,6 @@
     "@types/qrcode": "^1.5.6",
     "drizzle-kit": "^0.30.0",
     "typescript": "^5.7.0"
-  }
+  },
+  "license": "AGPL-3.0"
 }

apps/docs/package.json

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

apps/web/package.json

@@ -31,5 +31,6 @@
     "tailwindcss": "^4.0.0",
     "typescript": "^5.7.0",
     "vite": "^6.0.0"
-  }
+  },
+  "license": "AGPL-3.0"
 }