Copilot / contributor instructions for v0

- When adding new source or test files for v0, do NOT rely on wildcards. Add the file path explicitly to v0/include.mk in either V0_SRC (for library/source files) or V0_TEST (for test files beginning with `test_`).
- v0/include.mk is included by the top-level Makefile and is a dependency for object builds. Modifying v0/include.mk will force appropriate recompilation.

Example:
V0_SRC := v0/buffer.c v0/main.c
V0_TEST := v0/test.c v0/test_buffer.c