Enhance Renovate configuration (#2)

- Target main branch explicitly
- Set weekly schedule (weekends)
- Limit concurrent PRs to 10
- Group minor/patch updates for npm and github-actions to reduce PR noise

Ref: PRI-16

Co-authored-by: gandalf-the-greybeard[bot] <gandalf-the-greybeard[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

renovate.json

@@ -1,4 +1,19 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
-  "extends": ["config:recommended"]
+  "extends": ["config:recommended"],
+  "baseBranches": ["main"],
+  "schedule": ["every weekend"],
+  "prConcurrentLimit": 10,
+  "packageRules": [
+    {
+      "matchManagers": ["npm"],
+      "matchUpdateTypes": ["minor", "patch"],
+      "groupName": "npm minor and patch"
+    },
+    {
+      "matchManagers": ["github-actions"],
+      "matchUpdateTypes": ["minor", "patch"],
+      "groupName": "github-actions minor and patch"
+    }
+  ]
 }