fix: Add C# language detection to code extraction

Problem: System couldn't extract C# code examples from documentation
because the language detector only recognized C# from CSS classes
but failed to detect C# from code content.

Solution: Added C# heuristic detection patterns:
- 'using System' - System namespace imports
- 'namespace ' - Namespace declarations
- '{ get; set; }' - Property auto-property syntax
- 'public class ' - Public class declarations
- 'private class ' - Private class declarations
- 'internal class ' - Internal class declarations
- 'public static void ' - Static method declarations

Changes:
- cli/doc_scraper.py: Added C# patterns to detect_language() method
- tests/test_scraper_features.py: Added 7 comprehensive C# detection tests

Test Results: 409 passed (+7 new tests), 3 skipped, 0 failed

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/test_scraper_features.py

@@ -195,6 +195,62 @@ class TestLanguageDetection(unittest.TestCase):
         lang = self.converter.detect_language(elem, 'x')
         self.assertEqual(lang, 'python', 'Should detect python from bare class name')
 
+    def test_detect_csharp_from_using_system(self):
+        """Test C# detection from 'using System' keyword"""
+        html = '<code>using System;\nnamespace MyApp { }</code>'
+        elem = BeautifulSoup(html, 'html.parser').find('code')
+        code = elem.get_text()
+        lang = self.converter.detect_language(elem, code)
+        self.assertEqual(lang, 'csharp', 'Should detect C# from using System')
+
+    def test_detect_csharp_from_namespace(self):
+        """Test C# detection from 'namespace' keyword"""
+        html = '<code>namespace MyNamespace\n{\n    public class Test { }\n}</code>'
+        elem = BeautifulSoup(html, 'html.parser').find('code')
+        code = elem.get_text()
+        lang = self.converter.detect_language(elem, code)
+        self.assertEqual(lang, 'csharp', 'Should detect C# from namespace')
+
+    def test_detect_csharp_from_property_syntax(self):
+        """Test C# detection from property syntax"""
+        html = '<code>public string Name { get; set; }</code>'
+        elem = BeautifulSoup(html, 'html.parser').find('code')
+        code = elem.get_text()
+        lang = self.converter.detect_language(elem, code)
+        self.assertEqual(lang, 'csharp', 'Should detect C# from { get; set; } syntax')
+
+    def test_detect_csharp_from_public_class(self):
+        """Test C# detection from 'public class' keyword"""
+        html = '<code>public class MyClass\n{\n    private int value;\n}</code>'
+        elem = BeautifulSoup(html, 'html.parser').find('code')
+        code = elem.get_text()
+        lang = self.converter.detect_language(elem, code)
+        self.assertEqual(lang, 'csharp', 'Should detect C# from public class')
+
+    def test_detect_csharp_from_private_class(self):
+        """Test C# detection from 'private class' keyword"""
+        html = '<code>private class Helper { }</code>'
+        elem = BeautifulSoup(html, 'html.parser').find('code')
+        code = elem.get_text()
+        lang = self.converter.detect_language(elem, code)
+        self.assertEqual(lang, 'csharp', 'Should detect C# from private class')
+
+    def test_detect_csharp_from_public_static_void(self):
+        """Test C# detection from 'public static void' keyword"""
+        html = '<code>public static void Main(string[] args)\n{\n    Console.WriteLine("Test");\n}</code>'
+        elem = BeautifulSoup(html, 'html.parser').find('code')
+        code = elem.get_text()
+        lang = self.converter.detect_language(elem, code)
+        self.assertEqual(lang, 'csharp', 'Should detect C# from public static void')
+
+    def test_detect_csharp_from_class_attribute(self):
+        """Test C# detection from CSS class attribute"""
+        html = '<code class="language-csharp">var x = 5;</code>'
+        elem = BeautifulSoup(html, 'html.parser').find('code')
+        code = elem.get_text()
+        lang = self.converter.detect_language(elem, code)
+        self.assertEqual(lang, 'csharp', 'Should detect C# from language-csharp class')
+
 
 class TestPatternExtraction(unittest.TestCase):
     """Test pattern extraction from documentation"""