ci: fix PR title check for acronyms and fork PRs (#88)

- Switch trigger from pull_request to pull_request_target so the check
  can write PR labels on fork-originated PRs (safe because this workflow
  only reads the PR title, never checks out fork code)
- Relax subjectPattern to allow all-caps acronyms (SHA, API, URL) while
  still blocking Title Case starts (Add, Update)
- Add revert and build to CONTRIBUTING.md valid types list
- Document subject casing rule and PR title enforcement in CONTRIBUTING.md

Author: stevenobiajulu

.github/workflows/pr-title.yml

@@ -1,7 +1,7 @@
 name: PR Title Lint
 
 on:
-  pull_request:
+  pull_request_target:
     types: [opened, edited, synchronize, reopened]
     branches: [main]
 
@@ -31,15 +31,18 @@ jobs:
             revert
             build
           requireScope: false
-          subjectPattern: ^[a-z].+$
+          subjectPattern: ^(?![A-Z][a-z]).+$
           subjectPatternError: |
-            The subject must start with a lowercase letter.
+            The subject must not start with a Title Case word (e.g. "Add", "Update").
+            Acronyms like SHA, API, URL are fine. Lowercase starts are fine.
 
             Examples of valid PR titles:
               feat(docx-core): add paragraph diffing
               fix: correct bookmark cleanup order
               chore(release): bump workspace versions
               ci: add PR title validation
+              ci: SHA-pin all GitHub Actions
+              feat: API migration to v2
 
   auto-label:
     name: Apply type label from PR title

CONTRIBUTING.md

@@ -46,7 +46,7 @@ Longer is better — think essay, not tweet.
 Fixes: #42
 ```
 
-**Valid types:** `feat`, `fix`, `refactor`, `test`, `docs`, `chore`, `ci`, `perf`, `style`
+**Valid types:** `feat`, `fix`, `refactor`, `test`, `docs`, `chore`, `ci`, `perf`, `style`, `revert`, `build`
 
 **Scopes** should match the package or area you're changing:
 - `fix(docx-core):` — bug fix in the core OOXML library
@@ -56,10 +56,14 @@ Fixes: #42
 
 Scope your commits to one package when possible. Cross-package changes should use the primary package as scope.
 
+**Subject casing:** The subject (the part after the colon) must not start with a Title Case word like "Add" or "Update". Lowercase starts and all-caps acronyms (SHA, API, URL) are fine.
+
 **Reference issues** in the commit body: `Fixes: #N` (closes the issue) or `Ref: #N` (related but doesn't close).
 
 ## Pull Request Guidelines
 
+Pull request titles follow the same Conventional Commits format as commit messages. A CI check (`Validate conventional title`) enforces this on every PR.
+
 - **Keep PRs small and focused.** 10 small PRs are better than 1 monolithic one.
 - **A PR doesn't have to be done** — or even work — but it should represent clean progress in one direction.
 - **Decompose where possible.** For example, submit regexes + tests in one PR, then the feature that uses them in another.