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/parse-worker.ts

@@ -20,7 +20,7 @@ parentPort!.on('message', async (msg: { type: string; id?: number; filePath?: st
   } else if (msg.type === 'parse') {
     const { id, filePath, content } = msg;
     try {
-      const language = detectLanguage(filePath!);
+      const language = detectLanguage(filePath!, content);
       const result: ExtractionResult = extractFromSource(filePath!, content!, language);
 
       // Periodic parser reset to reclaim WASM heap memory