chore: Add development rule covering TDD, self-check and line wrap

Author: hanatyan128

.claude/rules/development.md

@@ -0,0 +1,17 @@
+# Development Rules
+
+When writing code, follow these rules.
+
+## Test policy
+
+- **If the project has a test suite, implement using TDD.** Write the test first, then proceed in red → green → refactor order.
+- **If the project has no test suite, manually verify after implementation.** Confirm there are no defects in the expected cases before marking the work complete.
+
+## Self-check after completion
+
+- **After the code is complete, re-check that it does not violate the comment discipline in [comment.md](comment.md).** If you also edited AI-facing prompts, re-check against [prompt.md](prompt.md) as well.
+- **If the project has a test suite, run the tests after the code is complete.** Do not mark the work complete until you have confirmed there are no errors or failures.
+
+## Formatting
+
+- **Wrap code at a reasonable line length.** Target a maximum of around 100 characters per line.