v0.2.0

Restructure as C library with CMake build system

- Promote wincanlib to primary library target (include/wincan/wincan.h, src/wincanlib.c)
- Replace Makefile with CMake; tools built with -DWINCAN_BUILD_TOOLS=ON
- Add shared USB device handle registry so multiple channels can be opened on the same adapter
- Rename wincan combined tool to canboth
- Migrate all tools to new wincan_bus_t / wincan_frame_t API
- Add FetchContent-compatible install rules for use in other CMake projects
- Add dual-channel example showing two independent bus handles on one device
- Update CI to publish tools zip and library zip as separate release assets

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>