docs: add commit rules to claude.md

CLAUDE.md

@@ -2,6 +2,15 @@
 
 ## Style
 
+- Keep everything short: replies, explanations, comments, docs.
 - Use simple English: short sentences, common words.
 - Avoid em dashes (—). Do not just swap them for "-" either. Rewrite the sentence instead, for
   example with a comma, a colon, brackets or two sentences.
+
+## Commits
+
+- English only.
+- Conventional Commits prefix: `feat:`, `fix:`, `chore:`, `docs:`, `refactor:`, `ci:`, `build:`.
+- Subject as short as possible. Imperative, lowercase, no trailing period.
+- Body only when something genuinely cannot be inferred from the diff.
+- Never add `Co-Authored-By`, "Generated with" or any other AI attribution to commits or PR descriptions.