Switch from squash merges to regular merge commits

Squash merges caused orphaned commits when pushing after auto-merge.
Regular merges preserve full commit history and avoid this issue.

- Disabled squash and rebase merge on repo settings
- Updated automerge action: MERGE_METHOD squash → merge
- Updated CLAUDE.md workflow docs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/automerge.yml

@@ -24,6 +24,6 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           MERGE_LABELS: "automerge"
-          MERGE_METHOD: "squash"
+          MERGE_METHOD: "merge"
           MERGE_DELETE_BRANCH: "true"
           UPDATE_METHOD: "rebase"