feat(claude/CLAUDE.md): expand git commits and add pull requests section

Commit messages and PR descriptions that explain "why" lead to better
code review and future archaeology. This adds guidance to prioritize
motivation over technical details, and asks for clarification when the
reason for a change isn't clear.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

claude/CLAUDE.md

@@ -67,6 +67,18 @@ Below are rules to follow with everything you do.
 
 - Prefer conventional commits format (e.g., `feat:`, `fix:`, `refactor:`), but
   defer to project conventions if they differ.
+- Lead with "why" over "what". The diff shows what changed; the message should
+  explain the motivation and purpose behind the change. If the "why" is not
+  clear, ask me before committing.
+- The commit body should start with the reason for the change. Technical
+  overview/details and implementation notes come after.
+
+## Pull Requests
+
+- PR descriptions should lead with "why" context, same as commits. Explain the
+  motivation and purpose before diving into technical details.
+- Use conventional commits format for PR titles when the repo follows
+  conventional commits.
 
 ## Dependencies