policies: add standard policy files, linting, formatting

- Add .editorconfig, .eslintrc.json, .prettierrc, .prettierignore, .dockerignore, .gitignore
- Add Makefile with lint, fmt, fmt-check, secret-scan, test (skip) targets
- Add package.json with eslint@^8.56.0, eslint-plugin-security, prettier
- Add tools/secret-scan.sh
- Fix unused variable (fs -> _fs)
- Auto-format with prettier
- make check passes clean (0 errors, 11 warnings)

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true