docs: add file and directory naming rules to CLAUDE.md

Document snake_case for file names and Go convention (no separators)
for package directory names. All existing names are already compliant.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -51,6 +51,13 @@ LEFT JOIN cuisine_translations ct ON ct.cuisine_slug = c.slug AND ct.lang = $lan
 When adding a new entity with text fields, always create a `{table}_translations`
 companion table and use LEFT JOIN COALESCE in all read queries.
 
+## File and Directory Naming
+
+- **File names:** snake_case — `token_verifier.go`, `wire_gen.go`, `entity.go`.
+- **Package directories:** lowercase, no separators — follow Go convention
+  (`savedrecipe/`, `openai/`, `infra/`). Do not use underscores in package names.
+- **Non-package directories** (migrations, docs, scripts): snake_case is acceptable.
+
 ## Naming
 
 **No abbreviated variable names.** Variables must use full descriptive names.