docs: add English commit convention to project

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Author: blogcompany0

.claude/CLAUDE.md

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+## Commit Convention
+- All commit messages MUST be written in English
+- Follow Conventional Commits: `<type>(<scope>): <subject>`
+- type: feat, fix, refactor, test, docs, chore, style, perf, ci, build
+- subject in imperative present tense (e.g. "add", "change", "fix")
+- One logical change per commit