fix: add file extension filtering to affected test mapper

- Skip non-code files (images, docs, etc.) in test mapping
- Prevents running all tests for non-code file changes
- Improves test performance

Author: jdalton

scripts/utils/affected-test-mapper.mjs

@@ -48,6 +48,13 @@ const RUN_ALL_PATTERNS = [
 function mapSourceToTests(filepath) {
   const normalized = normalizePath(filepath)
 
+  // Skip non-code files
+  const ext = path.extname(normalized)
+  const codeExtensions = ['.js', '.mjs', '.cjs', '.ts', '.cts', '.mts', '.json']
+  if (!codeExtensions.includes(ext)) {
+    return []
+  }
+
   // Core utilities affect all tests
   if (CORE_FILES.some(f => normalized.includes(f))) {
     return ['all']