refactor(skills): rename commit-message to commit

Renames the commit-message skill to commit:

- Moves commit-message/SKILL.md to commit/
- Updates the skill name in the SKILL.md frontmatter
- Updates the name and path in skills.json

The skill's behaviour is unchanged; only its identifier changes.

skills.json

@@ -9,11 +9,11 @@
       "path": "british-english"
     },
     {
-      "name": "commit-message",
+      "name": "commit",
       "description": "Generate well-formatted git commit messages following conventional commits",
       "repository": "https://onixbyte.dev/onixbyte/claude-code-skills",
       "branch": "main",
-      "path": "commit-message"
+      "path": "commit"
     },
     {
       "name": "spring-boot",