fix(ci): group Dependabot updates into one PR per ecosystem (#127)

This repo's `dependabot.yml` has no `groups:` block, so **Dependabot
opens one PR per dependency**.

Each of those PRs re-fires *every* workflow in the repo. So one
estate-wide bump — say `actions/checkout` 7.0.0 → 7.0.1 — fans out into
N PRs × M workflow runs worth of notifications. Combined with workflows
that fail, that is a large amplifier of the notification flood.

### Fix

Add `groups:` with `patterns: ["*"]`, so the same bump arrives as a
**single** PR:

```yaml
    groups:
      github-actions:
        patterns:
          - "*"
```

This matches the **223 estate repos that already group** (exemplar:
`aerie`). 50 did not — this is one of them.

Update frequency and ecosystems are unchanged; only the PR batching
changes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

.github/dependabot.yml

@@ -6,4 +6,11 @@ updates:
     schedule:
       interval: "daily"
     open-pull-requests-limit: 10
+    # Batch this ecosystem into a single PR. Ungrouped, Dependabot
+    # opens one PR per dependency, and each PR re-fires every
+    # workflow in the repo.
+    groups:
+      github-actions:
+        patterns:
+          - "*"