ci: add PR overlap detection workflow

Automatically detects potential merge conflicts between open PRs:

- Triggered on PR open/push to dev or master
- Compares changed files and line ranges across open PRs
- Tests actual merge conflicts by attempting merges
- Posts a comment on the PR with:
  - 🔴 Confirmed merge conflicts (with file paths and conflict sizes)
  - 🟠 High risk overlaps (>20 lines overlap)
  - 🟡 Medium risk overlaps
  - 🟢 Low risk (file overlap only)
- Shows conflict types (content, added, deleted, etc.)
- Includes last-updated timestamps for each PR

This helps contributors coordinate and resolve conflicts proactively.

.github/workflows/pr-overlap-check.yml

@@ -0,0 +1,37 @@
+name: PR Overlap Detection
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+    branches:
+      - dev
+      - master
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  check-overlaps:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0  # Need full history for merge testing
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Configure git
+        run: |
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git config user.name "github-actions[bot]"
+
+      - name: Run overlap detection
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          python .github/scripts/detect_overlaps.py ${{ github.event.pull_request.number }}