chore(renovate): automerge non-major dependency updates

Copy the automerge packageRules pattern from meshtastic/kzstd so green
minor/patch/pin/digest PRs land without manual merges; major updates
still require review.

Closes part of #10.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: jamesarich

renovate.json

@@ -2,5 +2,17 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
     "config:recommended"
+  ],
+  "packageRules": [
+    {
+      "description": "Automerge non-major dependency updates",
+      "matchUpdateTypes": ["minor", "patch", "pin", "digest"],
+      "automerge": true
+    },
+    {
+      "description": "Disable automerge for major updates",
+      "matchUpdateTypes": ["major"],
+      "automerge": false
+    }
   ]
 }