fix(security): prevent CWE-134 format string injection

- add "%s" to unsafe cons_show/log_*/win_println calls
- add check-cwe134.sh static analysis script
- integrate security check into CI pipeline

Closes #85

CONTRIBUTING.md

@@ -144,6 +144,16 @@ scan-build make
 scan-view ...
 ```
 
+### Security checks
+
+We have a static analyzer `check-cwe134.sh` that detects CWE-134 format string vulnerabilities. It runs automatically in CI but you can also run it locally:
+
+```bash
+./check-cwe134.sh
+```
+
+This checks for unsafe patterns where user-controlled data could be passed directly as a format string to functions like `cons_show`, `log_error`, `win_println`, etc. Always use `"%s"` format specifier when printing user data.
+
 ### Finding typos
 
 We include a `.codespellrc` configuration file for `codespell` in the root directory.