fix(build): keep Receiver bundle self-contained

[Betafer]

Summary

• give the copied SDL3 runtime an app-relative install name
• inspect the Receiver executable and every bundled dylib after packaging
• fail the build if any /opt/homebrew or /usr/local dependency remains

Why

The Receiver may be built on one Mac and installed on another. dylibbundler rewrites normal Mach-O dependencies, but SDL2 compatibility loads SDL3 dynamically, so that runtime needs an explicit internal identity and an independent bundle-integrity check.

Validation

• built a complete TargetBridge Receiver.app
• verified the bundle with codesign --verify --deep --strict
• verified SDL3 identity is @executable_path/../Frameworks/libSDL3.dylib
• independently scanned the executable and every bundled dylib: no external Homebrew paths remain

This PR changes one packaging script only.