ci: Add GH workflow to validate PR titles follow Conventional Commits.

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,9 @@
 <!--
-Set the PR title to a meaningful commit message in imperative form. E.g.:
-
-clp-s: Don't add implicit wildcards ('*') at the beginning and the end of a query (fixes #390).
+Set the PR title to a meaningful commit message that:
+- follows the Conventional Commits specification (https://www.conventionalcommits.org).
+- is in imperative form.
+Example:
+fix: Don't add implicit wildcards ('*') at the beginning and the end of a query (fixes #390).
 -->
 
 # Description

.github/workflows/clp-pr-title-checks.yaml

@@ -0,0 +1,23 @@
+name: "clp-pr-title-checks"
+
+on:
+  pull_request_target:
+    types: ["edited", "opened", "reopened"]
+    branches: ["main"]
+
+concurrency:
+  group: "${{github.workflow}}-${{github.ref}}"
+
+  # Cancel in-progress jobs for efficiency
+  cancel-in-progress: true
+
+jobs:
+  conventional-commits:
+    permissions:
+      # For amannn/action-semantic-pull-request
+      pull-requests: "read"
+    runs-on: "ubuntu-latest"
+    steps:
+      - uses: "amannn/action-semantic-pull-request@v5"
+        env:
+          GITHUB_TOKEN: "${{secrets.GITHUB_TOKEN}}"