feat: support user-defined functions and classes in Ren'Py python

- Converter: def/return/global/nonlocal, class (inheritance, property,
  staticmethod, classmethod), lambda, *args/**kwargs and call-site unpacking.
  Unsupported dunder methods, generators and unknown decorators are still refused
- Player: closures, super(), instances that survive save/load, isinstance,
  hasattr/getattr/setattr, map/filter/sorted(key=), recursion limit
- audit_ir accepts calls to names, classes and methods the game defines itself;
  unknown renpy.* calls still block the import. Volume/pan/pause/replay calls
  are accepted as presentation-only no-ops; build.* settings are skipped
- Tests: IR fixture compiled from tests/fixtures/classes.py (tests/make_ir.py)
  and run in the interpreter; converter tests updated

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/app/converter/rpy_parser.py

@@ -373,6 +373,9 @@ class RpyParser:
                 except ValueError:
                     pass
                 continue
+            if (isinstance(node, ast.Expr) and isinstance(node.value, ast.Call)
+                    and ast.unparse(node.value.func).startswith("build.")):
+                continue  # distribution build settings (build.classify, build.name ...), no gameplay
             try:
                 self.d.init_code.extend(pyexpr.stmt(node))
             except Unsupported as e: