feat: pure C API isolation layer + automated publish pipeline

* feat: add pure C API isolation layer for cross-compiler compatibility

Introduce a pure C ABI boundary between the C++/Fortran core library
(wsjtx_core) and the Node.js N-API binding (.node). This solves the
Windows crash where MSVC-compiled Node.js failed to load MinGW-compiled
native extensions due to ABI incompatibility.

Architecture: .node (N-API) -> C ABI -> wsjtx_core shared library (C++/Fortran)

- New: native/wsjtx_c_api.h and .cpp (pure C interface with opaque handle)
- Modified: wsjtx_wrapper to use C API instead of C++ direct linking
- Rewritten: CMakeLists.txt with dual-target build (wsjtx_core + .node)
- Windows: two-phase build (MinGW core DLL + MSVC .node)
- Linux/macOS: single cmake build produces both targets
- CI workflow simplified from 773 to ~200 lines

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

* fix: add missing <stdexcept> include and fix macOS dylibbundler conflict

- Linux/macOS build failed because std::invalid_argument needs <stdexcept>
  (MSVC includes it transitively, GCC does not)
- macOS packaging failed because libwsjtx_core.dylib was manually copied
  before dylibbundler tried to copy it as a dependency. Removed manual copy,
  added build/Release to search paths, and use -of flag for overwrite safety.

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

* fix: remove redundant dylibbundler step causing self-copy error on macOS

dylibbundler already follows transitive dependencies when processing .node,
so it bundles libwsjtx_core.dylib and all its deps (fftw, gfortran, etc.)
in a single pass. The second dylibbundler call was redundant and failed
because it tried to copy already-bundled files onto themselves.

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

* feat: automate npm publish and GitHub Release via CI

- Add `publish` job to build.yml: triggers only on v* tag push,
  downloads prebuilds from collect-artifacts, validates all 5 platforms,
  runs npm publish, and creates GitHub Release with platform archives
- Simplify prepublishOnly to just build:ts (CI handles validation)
- Remove manual scripts/create-release.sh (now integrated in CI)
- Update PUBLISHING.md to reflect the new one-step workflow

New release flow: npm version patch && git push --tags → fully automated.

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

* ci: run full encode-decode cycle tests on all platforms

Add npm run test:full to CI test steps, which runs the comprehensive
test suite including FT8 encode→WAV→decode round-trip verification.
This ensures the native binaries actually work end-to-end, not just load.

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: boybook

.github/workflows/build.yml

@@ -1,9 +1,16 @@
 node_modules/
 build/
+build-mingw/
+build-core/
 prebuilds/
 dist/
+.idea/
+.claude/
 
 # FFTW wisdom files (machine-specific optimization cache)
 fftw_wisdom.dat
 *.wisdom
-hashtable.txt
+hashtable.txt
+
+# Build logs
+*.log