Compiler and docs on every system: macOS Intel in CI, releases made by CI, docs for vectors and --cpu

- CI: macOS on Apple Silicon and Intel (macos-15, macos-15-intel); a tag v* attaches every package
  (Linux x64/ARM64, macOS ARM64/x64, Windows x64, the VS Code extension) to its release
- vectors: fma is llvm.fmuladd (llvm.fma was a libm call per lane without FMA hardware: 3.5x slower)
- examples/simd.fch: a dot product eight at a time, timed against the plain loop
- README and the English guides: installing on Linux, macOS and Windows; vectors (SIMD); --cpu;
  -g is DWARF on Windows too (lldb from llvm-mingw); no more mention of the C++ compiler
- comments left from the C++ compiler (src/target.cpp, src/codegen.cpp, "never frees") brought up to date

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Psc42moPLwP43Cmb9oZqSR

runtime/finch_rt.c

@@ -2,7 +2,7 @@
 // It is embedded in the compiler, compiled once into a cache folder, and linked
 // statically into every Finch program. Everything here is plain C with no state.
 //
-// Layout shared with the compiler (src/codegen.cpp):
+// Layout shared with the compiler (src/gen.fch):
 //   str  = { char *ptr; int64 len; int64 cap }   ptr is always NUL-terminated
 //          cap > 0  : heap memory owned by the value (cap bytes allocated)
 //          cap == 0 : a string literal, valid forever, never written to