refactor: rename debug_issue tool to debug for brevity

- Rename debug_issue.py to debug.py
- Update tool name from 'debug_issue' to 'debug' throughout codebase
- Update all references in server.py, tests, and README
- Keep DebugIssueTool class name for backward compatibility
- All tests pass with the renamed tool

This makes the tool name shorter and more consistent with other
tool names like 'chat' and 'analyze'. The functionality remains
exactly the same.

🤖 Generated with Claude Code

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

tests/test_tools.py

@@ -103,7 +103,7 @@ class TestReviewCodeTool:
 
 
 class TestDebugIssueTool:
-    """Test the debug_issue tool"""
+    """Test the debug tool"""
 
     @pytest.fixture
     def tool(self):
@@ -111,7 +111,7 @@ class TestDebugIssueTool:
 
     def test_tool_metadata(self, tool):
         """Test tool metadata"""
-        assert tool.get_name() == "debug_issue"
+        assert tool.get_name() == "debug"
         assert "DEBUG & ROOT CAUSE ANALYSIS" in tool.get_description()
         assert tool.get_default_temperature() == 0.2
 
@@ -232,8 +232,8 @@ class TestAbsolutePathValidation:
         assert "../parent/file.py" in response["content"]
 
     @pytest.mark.asyncio
-    async def test_debug_issue_tool_relative_path_rejected(self):
-        """Test that debug_issue tool rejects relative paths"""
+    async def test_debug_tool_relative_path_rejected(self):
+        """Test that debug tool rejects relative paths"""
         tool = DebugIssueTool()
         result = await tool.execute(
             {