fix(pty): switch to @homebridge/node-pty-prebuilt-multiarch fork

Resolves "Failed to load PTY module" install errors on Linux/macOS by
aliasing node-pty to the homebridge fork, which ships prebuilds for
linux x64/arm64/arm/ia32 across many Node ABIs and uses prebuild-install
for darwin/windows binaries on install.

- Aliased dep so all "node-pty" import specifiers (and vi.mock calls)
  keep working unchanged.
- Removed darwin chmod postinstall hack (fork handles permissions).
- Updated cli/build.ts to dynamically resolve node-pty install root and
  pick prebuilds by ABI for Linux cross-compile; warn-and-skip for
  darwin/windows cross-compile (host-only there, as before).
- Added type shim because the fork's bundled typings declare module
  '@homebridge/node-pty-prebuilt-multiarch', not 'node-pty'.

Verified: pnpm install clean, dashboard typecheck clean, native module
loads and spawns shell via fork, host + linux-x64 cross-compile staging
both produce dist/runtime/<plat>/pty.node.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -50,6 +50,7 @@
   },
   "pnpm": {
     "onlyBuiltDependencies": [
+      "@homebridge/node-pty-prebuilt-multiarch",
       "electron",
       "esbuild",
       "koffi",