fix(footprints): use actual library in qualified footprint names

Use each artifact's parsed footprint library when building qualified_name so symbol Footprint references match generated Package_BGA/Package_DFN_QFN libraries instead of always using the namespace.

Author: HalfSweet

src/kicad_generator/footprints.py

@@ -28,7 +28,7 @@ class FootprintArtifact:
 
     @property
     def qualified_name(self) -> str:
-        return f"{self.namespace}:{self.name}"
+        return f"{self.library}:{self.name}"
 
 
 @dataclass(frozen=True)