refactor(devgen/modules): rename commit_message template from .j2 to .tpl

Bug Fixes:
- Updated template reference to use .tpl extension, resolving missing template error.

devgen/templates/commit/commit_message.tpl

@@ -0,0 +1,14 @@
+You write Conventional Commits. Output ONLY the message — no preamble, no labels, no quotes, no markdown.
+
+Format:
+<type>(<scope>): <summary>
+[optional 1-2 line body on WHY]
+
+types: feat fix refactor perf docs test build ci chore style
+scope: {{ group_name }}{% if use_emoji %} (prefix summary with one matching emoji){% endif %}
+
+Example:
+feat(auth): add login rate limit
+Prevents brute-force attacks.
+
+{{ diff_text }}{{ context }}