Enhanced Textual TUI with proper API usage and documentation

- Fixed DataTable row selection and event handling
- Added explicit column keys to prevent auto-generated keys
- Implemented row-to-flow mapping for reliable selection tracking
- Converted left metrics panel to horizontal top bar
- Fixed all missing FlowStats/EnhancedAnalysisData attributes
- Created comprehensive Textual API documentation in Documentation/textual/
- Added validation checklist to prevent future API mismatches
- Preserved cursor position during data refreshes
- Fixed RowKey type handling and event names

The TUI now properly handles flow selection, displays metrics in a compact top bar,
and correctly correlates selected rows with the details pane.

test_textual.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+"""
+Test script for Textual TUI interface
+"""
+
+import sys
+import os
+
+# Add the analyzer package to the path
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..'))
+
+from analyzer.analysis.core import EthernetAnalyzer
+from analyzer.tui.textual.app_v2 import StreamLensAppV2
+
+def main():
+    """Test the Textual interface with mock data"""
+    
+    # Create analyzer with some sample data
+    analyzer = EthernetAnalyzer(enable_realtime=False)
+    
+    # Create and run the Textual app V2
+    app = StreamLensAppV2(analyzer)
+    app.run()
+
+if __name__ == "__main__":
+    main()