Vendor esp-idf-rc522 as plain source instead of submodule

The library is modified (NDEF reading, cascade anticollision) so vendoring
it directly avoids needing push access to the upstream fork.

https://claude.ai/code/session_01MhAnh68DPNnTjcKqjNYDmk

device/components/esp-idf-rc522/CMakeLists.txt

@@ -0,0 +1,4 @@
+idf_component_register(
+    SRCS "rc522.c"
+    INCLUDE_DIRS "."
+)