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/tree-sitter.ts

@@ -106,7 +106,7 @@ export class TreeSitterExtractor {
   constructor(filePath: string, source: string, language?: Language) {
     this.filePath = filePath;
     this.source = source;
-    this.language = language || detectLanguage(filePath);
+    this.language = language || detectLanguage(filePath, source);
     this.extractor = EXTRACTORS[this.language] || null;
   }
 
@@ -2087,7 +2087,7 @@ export function extractFromSource(
   source: string,
   language?: Language
 ): ExtractionResult {
-  const detectedLanguage = language || detectLanguage(filePath);
+  const detectedLanguage = language || detectLanguage(filePath, source);
   const fileExtension = path.extname(filePath).toLowerCase();
 
   // Use custom extractor for Svelte