[examples] Add shapes_recursive_tree

[Jopestpe]

Description

• Adds a basic recursive tree example with GUI controls, showing:
• Recursive branching with adjustable angle, thickness, and decay
• Optional Bezier-style branches
• Real-time modification via GUI sliders and checkbox

Changelog

• Added examples/shapes/shapes_recursive_tree.c - example code
• Added examples/shapes/shapes_recursive_tree.png - screenshot
• Updated Makefile, README.md, and examples_list.txt

Tested and compiles successfully on Linux

[raysan5]

Please, could you format it with declaration/definition for function, similar to: https://github.com/raysan5/raylib/blob/master/examples/shapes/shapes_double_pendulum.c

Also, I'm not a big fan of recursion, is it possible to reimplement it in a more portable and self-contained function? Depending on globals and recursion is not portable... but if no possible to find another solution it's ok...