ci: install safe-paths auto-merge (#5)

Adds the safe-paths auto-merge caller from `topcoder1/ci-workflows`.

**What this enables:**
- PRs whose diff touches **only** safe paths (`docs/**`, `tests/**`,
`test_*.py`, `*_test.*`, `*.test.*`, `*.spec.*`, `**/__tests__/**`) get
`gh pr merge --auto --squash` called automatically — any author.
- All-or-nothing: any one unsafe path defers to
`claude-author-automerge.yml` or manual click.
- Branch protection still applies — required checks must pass before
auto-merge fires.

**Why this is safe:**
- Docs have zero runtime impact.
- Tests cannot break runtime (failing tests do not ship; passing tests
do not change behavior).
- Maintainers click-merging typo fixes and test additions is
alarm-fatigue-by-design — the path classification IS the safety
argument.

**Auto-merge rationale:** workflow file → manual click-merge per
CLAUDE.md. The whole point of the workflow being installed is to handle
*future* docs/tests-only PRs — not this one.

🤖 Auto-installed via
[install-safe-paths-automerge.sh](https://github.com/topcoder1/dotclaude/blob/main/templates/ci-workflows/scripts/install-safe-paths-automerge.sh)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: topcoder1

.github/workflows/safe-paths-automerge.yml

@@ -0,0 +1,30 @@
+name: Safe-paths Auto-merge
+
+# Auto-enables `gh pr merge --auto --squash` on any PR (any author) whose
+# diff touches ONLY safe paths (docs, tests, test_*.py / *_test.* /
+# *.test.* / *.spec.* / **/__tests__/**). All-or-nothing: one unsafe
+# file in the diff and this workflow no-ops, deferring to
+# claude-author-automerge.yml (or manual click).
+#
+# Branch protection's required-status-checks still apply — auto-merge
+# waits for them. Reusable defined at:
+#   topcoder1/ci-workflows/.github/workflows/safe-paths-automerge.yml
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, ready_for_review]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+concurrency:
+  group: safe-paths-automerge-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  automerge:
+    uses: topcoder1/ci-workflows/.github/workflows/safe-paths-automerge.yml@main
+    secrets: inherit
+    with:
+      merge_method: squash