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

src/cimport.fch

@@ -1,10 +1,9 @@
 // C headers, read through libclang, written in Finch.
 //
 // What `import "stdio.h"` teaches the compiler: the C functions, the constants (enum values and
-// plain #define numbers), the extern variables (stdout) and the structs. The same job as
-// src/cimport.cpp, done by calling libclang's C API through Finch's own C import -- which is
-// what makes this the part that closes the bootstrap: to compile this file the self-hosted
-// compiler has to read libclang's headers with this very code.
+// plain #define numbers), the extern variables (stdout) and the structs. It calls libclang's C API
+// through Finch's own C import -- so to compile this file, the compiler reads libclang's headers
+// with this very code.
 //
 // C structs by value appear in types as the named type `module "C"`.
 import ast