chore(deps): group dependabot updates with a 7 day cooldown (#35)

# Why

Groups every Dependabot ecosystem into one PR, adds a 7 day cooldown so
short-lived releases are skipped, and sets an explicit `chore(deps)`
prefix. Majors are grouped too, so a breaking bump holds back the whole
group.

# Risks

No Risks Found

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: icco

.github/dependabot.yml

@@ -5,15 +5,35 @@ updates:
     schedule:
       interval: weekly
     groups:
-      opencode:
+      npm:
         patterns:
-          - '@opencode/*'
+          - '*'
+    commit-message:
+      prefix: chore(deps)
+      prefix-development: chore(deps-dev)
+    cooldown:
+      default-days: 7
   - package-ecosystem: docker
     directory: /
-    open-pull-requests-limit: 10
     schedule:
       interval: weekly
+    commit-message:
+      prefix: chore(deps)
+    cooldown:
+      default-days: 7
+    groups:
+      docker:
+        patterns:
+          - '*'
   - package-ecosystem: github-actions
     directory: /
     schedule:
       interval: weekly
+    commit-message:
+      prefix: chore(deps)
+    cooldown:
+      default-days: 7
+    groups:
+      github-actions:
+        patterns:
+          - '*'