fix(build): make macOS release builds work natively

The --mac-release path (full-node and --lite-backend) had never run on a real
Mac and broke on several Linux-only assumptions:

- build.sh version parser used GNU sed \+ (BSD sed reads it literally), so it
  aborted before compiling — switched to POSIX [[:space:]][[:space:]]*.
- build.sh libsodium universal check used GNU grep \| — switched to grep -E.
- libwebp's cpu.cmake applies -mno-sse2 to its reference DSP files; under a
  universal build (-arch arm64;x86_64) that lands on the x86_64 slice, where it
  disables _Float16 and breaks the SDK 26 <math.h>. Added an idempotent
  FetchContent PATCH_COMMAND (cmake/patch-libwebp-simd.cmake) to neutralize it.
- The SDXL lite backend static lib needs Security + CoreFoundation frameworks on
  macOS; added them to the imported dragonx_lite_backend target for APPLE.
- Added a DRAGONX_MAC_ARCHS override plus auto-detect: with --lite-backend the
  app is built for the arch(es) the backend .a actually provides (its pinned
  ring 0.16.11 is x86_64-only), instead of failing to link a universal app.
- build-lite-backend-artifact.sh uses bash 4+ (mapfile); added a re-exec guard
  for macOS's stock bash 3.2 and added bash to setup.sh's macOS core deps.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

setup.sh

@@ -133,7 +133,7 @@ pkgs_core_arch="base-devel cmake git pkg-config
     libxkbcommon wayland libsodium curl
     autoconf automake libtool wget python xxd"
 
-pkgs_core_macos="cmake python xxd"
+pkgs_core_macos="bash cmake python xxd"
 
 # Windows cross-compile (from Linux)
 pkgs_win_debian="mingw-w64 zip"