docs: add CLAUDE.md developer guide

Add comprehensive developer documentation for Claude Code assistance,
covering project architecture, command framework, entity models, UX
components, build/release process, and common development patterns.

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

Author: fxck

.gitignore

@@ -14,3 +14,6 @@ tools/npm/node_modules
 *.DS_Store
 # ignore built binary in root dir
 /zcli
+
+# claude code local settings
+.claude/settings.local.json