chore: add pull request title validator (#126)

.github/pull_request_template.md

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+<!-- ## Title Guidelines
+
+A title always has a prefix and a subject.
+
+### Prefix
+Make sure the title is prefixed with one of the following:
+
+| Prefix | When to use |
+|--------|-------------|
+| `feat:`     | New feature |
+| `fix:`      | Bug fix |
+| `docs:`     | Documentation only changes |
+| `style:`    | Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc) |
+| `refactor:` | Code changes that neither fixes a bug nor adds a feature |
+| `perf:`     | Code change that improves performance |
+| `test:`     | Adding missing or correcting existing tests |
+| `chore:`    | Changes to the build process or auxiliary tools and libraries such as documentation generation, ci, etc |
+
+### Subject
+
+Ensure the subject contains succinct description of the change.
+* Use the imperative, present tense: "change", not "changed" nor "changes"
+* Don’t capitalize first letter
+* No dot (.) at the end
+-->

.github/workflows/pull-request-title-validator.yml

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+name: "Pull Request Title Validator"
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - edited
+      - synchronize
+      - reopened
+
+permissions:
+  pull-requests: read
+
+jobs:
+  # Ensure PR title matches Angular Commit Guidelines
+  validate-pr-title:
+    name: Validate PR title
+    runs-on: ubuntu-latest
+    steps:
+      - uses: amannn/action-semantic-pull-request@v5
+        with:
+          subjectPattern: ^(?![A-Z]).+(?<!\.)$
+          subjectPatternError: |
+            The subject "{subject}" found in the pull request title "{title}"
+            didn't match the configured pattern. Please ensure that the subject
+            doesn't start with an uppercase character and doesn't end with a period.
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}