Updates git message template.

Updates the .gitmessage file to follow the single-line subject guidelines.
This change enforces a more concise and standardized commit message format, improving readability and maintainability.

Author: yoeunes

.gitmessage

@@ -1,3 +1,6 @@
-# type(scope): description
-#
-# Types: feat, fix, docs, style, refactor, perf, test, build, ci, chore
+# Single-line subject only. No body, no footer.
+# Use a short, capitalized, imperative description (<= 72 chars, no trailing period).
+# Examples:
+# Add verbose flag for regex parsing
+# Fix PHP 8.4 CI cache key
+Short imperative description