Add phase 4 settings migration workflow

Author: cagnulein

.github/workflows/settings-refactor-phase4.yml

@@ -0,0 +1,44 @@
+name: Settings refactor phase 4 migration
+
+on:
+  push:
+    branches:
+      - agent/settings-refactor-phase1-safety
+    paths:
+      - 'scripts/phase4_behavior_parity.py'
+      - 'tests/test_settings_behavior_parity.py'
+      - '.github/workflows/settings-refactor-phase4.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+jobs:
+  migrate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: agent/settings-refactor-phase1-safety
+          fetch-depth: 1
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+      - name: Apply Phase 4 migration
+        run: python3 scripts/phase4_behavior_parity.py
+      - name: Validate settings parity
+        run: |
+          python3 -m unittest tests/test_settings_audit.py tests/test_settings_behavior_migration.py tests/test_modern_settings_preview.py tests/test_settings_behavior_parity.py
+          python3 scripts/settings_audit.py --report settings-audit.json
+      - name: Commit Phase 4 migration
+        shell: bash
+        run: |
+          if git diff --quiet -- src/settings.qml src/settings-catalog.json; then
+            echo 'Phase 4 migration is already applied.'
+            exit 0
+          fi
+          git config user.name 'github-actions[bot]'
+          git config user.email '41898282+github-actions[bot]@users.noreply.github.com'
+          git add src/settings.qml src/settings-catalog.json
+          git commit -m 'Preserve legacy settings behavior in modern UI'
+          git push origin HEAD:agent/settings-refactor-phase1-safety