Restore the universal VST3 build, GUI example, and parameter store

[godofecht]

Reconstructs work that was destroyed by a git reset --hard on a dirty tree. It had never been committed, so none of it was recoverable from git.

Where possible this is recovered rather than guessed: stale artifacts left in zig-out from the last good build confirmed the exact target layout.

libDanzigGain_arm64.dylib   Mach-O 64-bit dynamically linked shared library arm64
libDanzigGain_x86.dylib     Mach-O 64-bit dynamically linked shared library x86_64
danzig-gain-ui              Mach-O 64-bit executable arm64
                            -> CoreAudio, CoreFoundation, WebKit

Universal VST3 bundle

Behind a vst3 step, since it doubles compile work and is macOS-only.

• Builds DanzigGain for aarch64-macos and x86_64-macos, merged with lipo so one bundle loads on either architecture
• Lays out Contents/{Info.plist,PkgInfo,MacOS/DanzigGain}
• install-vst3 copies it to ~/Library/Audio/Plug-Ins/VST3/

$ lipo -info zig-out/DanzigGain.vst3/Contents/MacOS/DanzigGain
Architectures in the fat file: ... are: x86_64 arm64

$ plutil -lint zig-out/DanzigGain.vst3/Contents/Info.plist
OK

GUI example

examples/danzig-gain-ui survived as untracked files but had no build wiring. A webview front end over CoreAudio, with ui/index.html embedded so the binary is self-contained. Needs the webview dependency, hence the new build.zig.zon. The Zig bindings are declarations only, so it links the dependency's webviewStatic artifact for the C++ implementation.

Parameter store

src/params.zig also survived untracked, but its re-exports in root.zig and its tests were lost, leaving it orphaned and unreachable. Both restored, taking the unit suite from 22 to 35 tests.

Verification

zig build              24/24 steps succeeded
zig build test          7/7 steps, 35/35 tests passed
zig build vst3        10/10 steps succeeded

🤖 Generated with Claude Code