CI: Build Success/Failure Status in PR Comments

## 🧩 Feature: CI Build Status in PR Comments

### Problem / Motivation
Contributors and reviewers currently need to open workflow logs manually to check build results.
This slows down the review process and reduces visibility of CI outcomes.

### Proposed Solution
- Automatically run build checks on each pull request.
- Post a comment in the PR with build status:
- ✅ **Success** — build passed
- ❌ **Failed** — include brief error logs
- Update or replace the comment automatically on workflow reruns.

### Alternatives Considered
Relying only on GitHub’s built-in status checks — visible but less informative within the PR conversation.

### Acceptance Criteria
- Workflow triggers on `pull_request`.
- Build results appear in PR comments.
- Comments update on new runs.