feat: Add content-based C++ detection for .h headers

Addresses C++ classes missing from .h files where extension-based detection defaults to 'c' language which has no class extraction support. Adds looksLikeCpp() heuristic that scans first 8KB for C++-specific patterns (namespace, class, template, access specifiers) to promote .h files to 'cpp' language when C++ constructs are detected. Ensures cpp grammar is loaded alongside c to handle potential .h promotion during parsing.

src/extraction/grammars.ts

@@ -174,9 +174,25 @@ export function getParser(language: Language): Parser | null {
 /**
  * Detect language from file extension
  */
-export function detectLanguage(filePath: string): Language {
+export function detectLanguage(filePath: string, source?: string): Language {
   const ext = filePath.substring(filePath.lastIndexOf('.')).toLowerCase();
-  return EXTENSION_MAP[ext] || 'unknown';
+  const lang = EXTENSION_MAP[ext] || 'unknown';
+
+  // .h files could be C or C++ — check source content for C++ features
+  if (lang === 'c' && ext === '.h' && source) {
+    if (looksLikeCpp(source)) return 'cpp';
+  }
+
+  return lang;
+}
+
+/**
+ * Heuristic: does a .h file contain C++ constructs?
+ * Checks the first ~8KB for patterns that are unique to C++ and never valid C.
+ */
+function looksLikeCpp(source: string): boolean {
+  const sample = source.substring(0, 8192);
+  return /\bnamespace\b|\bclass\s+\w+\s*[:{]|\btemplate\s*<|\b(?:public|private|protected)\s*:|\bvirtual\b|\busing\s+(?:namespace\b|\w+\s*=)/.test(sample);
 }
 
 /**