fix: address QA findings on detect-pipeline workflow

- Fix subdirectory matching: use prefix match for .github/* paths
  instead of exact dirname match (fixes .github/workflows/ not matching)
- Upgrade tj-actions/changed-files from v44 to v47 (Node 24 support)
- Extract detection logic into scripts/detect-pipeline.sh for testability
- Add 22 automated tests in scripts/test-detect-pipeline.sh covering
  infra-only, plugin code, mixed, and edge cases
- Add test-detection-logic CI job to run tests on every PR
- Update README.md to reference v47

cc @cpfarhood

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/README.md

@@ -68,7 +68,7 @@ Use `tj-actions/changed-files`:
 ```yaml
 - name: Get changed files
   id: changed-files
-  uses: tj-actions/changed-files@v44
+  uses: tj-actions/changed-files@v47
   with:
     files_separator: '\n'
 ```

.github/workflows/detect-pr-pipeline.yaml

@@ -10,6 +10,16 @@ permissions:
   pull-requests: write
 
 jobs:
+  test-detection-logic:
+    runs-on: runners-privilegedescalation
+    timeout-minutes: 2
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Run detection tests
+        run: bash scripts/test-detect-pipeline.sh
+
   detect-pipeline:
     runs-on: runners-privilegedescalation
     timeout-minutes: 5
@@ -24,7 +34,7 @@ jobs:
 
       - name: Get changed files
         id: changed-files
-        uses: tj-actions/changed-files@v44
+        uses: tj-actions/changed-files@v47
         with:
           files_separator: '\n'
 
@@ -34,34 +44,7 @@ jobs:
           echo "Changed files:"
           echo "${{ steps.changed-files.outputs.all_changed_files }}"
 
-          pipeline="pipeline-a"
-
-          if [ -n "${{ steps.changed-files.outputs.all_changed_files }}" ]; then
-            all_infra=true
-            while IFS= read -r file; do
-              filename=$(basename "$file")
-              dirname=$(dirname "$file")
-
-              if [ "$dirname" = ".github" ] || \
-                 [[ "$filename" == *.md ]] || \
-                 [[ "$filename" == .eslintrc* ]] || \
-                 [[ "$filename" == .prettierrc* ]] || \
-                 [[ "$filename" == renovate.json* ]] || \
-                 [[ "$filename" == .gitignore ]] || \
-                 [[ "$filename" == .editorconfig ]] || \
-                 [[ "$filename" == LICENSE ]]; then
-                continue
-              else
-                all_infra=false
-                echo "Non-infra file found: $file"
-                break
-              fi
-            done <<< "${{ steps.changed-files.outputs.all_changed_files }}"
-
-            if [ "$all_infra" = true ]; then
-              pipeline="pipeline-b"
-            fi
-          fi
+          pipeline=$(echo "${{ steps.changed-files.outputs.all_changed_files }}" | bash scripts/detect-pipeline.sh)
 
           echo "pipeline-type=$pipeline" >> $GITHUB_OUTPUT
           echo "Detected pipeline: $pipeline"