Fix canonical format of config/sms-sites.json

The sms-sites.json file was not in canonical format (sorted keys,
2-space indent, trailing newline), causing `npm run build` to fail
during the `check:content` step in Docker.

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

config/sms-sites.json

@@ -1,7 +1,9 @@
 {
   "sites": [
     {
-      "allowedSenders": ["+15035550100"],
+      "allowedSenders": [
+        "+15035550100"
+      ],
       "phoneNumber": "+15035550142",
       "repoRoot": ".",
       "siteId": "timber-and-grain"