Rewrite Python scripting documentation to match actual implementation

The previous docs described a fictional API (model global, @before_update/@after_update hooks, add_constraint, traverse) that doesn't exist. Replaced with accurate documentation covering the invoke(args) pattern, value expressions, model scripts, text expressions, dynamic groups, assign_property, environment variables, and available libraries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: johannesheesterman

docs/archer/Introduction.md

@@ -138,8 +138,8 @@ Archer modeling language supports function expressions, which allow you to perfo
 | `distinct` \| `alldiff` | Returns true if all arguments are distinct, otherwise returns false. |
 
 
-## Integrating with Python
-Archer allows direct integration with any Python script. For more information see [Python Integration with Archer](/docs/archer/python).
+## Python scripting
+Archer supports Python scripting for value expressions, model scripts, text expressions, and dynamic groups. For more information see [Python Scripting](/docs/archer/python).
 
 ## Common Mistakes