feat(theme): native macOS appearance detection via CoreFoundation FFI (#207)
Move macOS dark/light mode detection from compiled Objective-C helper
+ shell-out to defaults(1) into the Rust pi-natives crate.
Sync detection: CFPreferencesCopyAppValue reads AppleInterfaceStyle
directly — no subprocess, no shell.
Observer: background thread registers with CFDistributedNotificationCenter
for AppleInterfaceThemeChangedNotification. A 2-second CFRunLoopTimer
serves as both run-loop keep-alive and polling fallback (distributed
notifications may not reliably reach background threads on all macOS
versions). Dedup logic prevents double-firing.
Removes: MACOS_OBSERVER_OBJC constant, getOrCompileObserver(), binary
cache at ~/.omp/cache/, defaults read shell-out, readLines stream
parsing, fallback poll timer.
Adds: crates/pi-natives/src/appearance.rs (CoreFoundation FFI),
packages/natives/src/appearance/ (TS bindings).
