chore(dependabot): group @opencode-ai/* packages together (#46)

@opencode-ai/plugin (dependency) and @opencode-ai/sdk (devDependency)
are sibling packages that version-lock upstream. Currently split across
separate Dependabot group buckets, causing drift on sequential merge.

Add explicit pattern group '@opencode-ai/*' (listed before dev-dependencies
group so it takes precedence) to ensure both land in one PR.

Author: justin-carper

.github/dependabot.yml

@@ -6,6 +6,9 @@ updates:
       interval: "weekly"
     open-pull-requests-limit: 10
     groups:
+      opencode-ai:
+        patterns:
+          - "@opencode-ai/*"
       dev-dependencies:
         dependency-type: "development"