Fix BCORNE firmware build for vial-qmk on modern Python.

Include m57.c for RGB matrix linking, add Python 3.14 math patch and platform fallback, and keep brightness step in info.json only.

corne/firmware/patches/vial-qmk-math-py.patch

@@ -0,0 +1,15 @@
+--- a/lib/python/qmk/math.py
++++ b/lib/python/qmk/math.py
+@@ -23,8 +23,10 @@ def compute(expr):
+ 
+ 
+ def _eval(node):
+-    if isinstance(node, ast.Num):  # <number>
+-        return node.n
++    if isinstance(node, ast.Constant) and isinstance(node.value, (int, float, complex)):
++        return node.value
++    elif isinstance(node, ast.Num):  # <number> (Python <3.14)
++        return node.n
+     elif isinstance(node, ast.BinOp):  # <left> <operator> <right>
+         return operators[type(node.op)](_eval(node.left), _eval(node.right))
+     elif isinstance(node, ast.UnaryOp):  # <operator> <operand> e.g., -1