fix(nix): natively compile and correctly stage node-pty for desktop app

- Add ELECTRON_SKIP_BINARY_DOWNLOAD=1 to nix/lib.nix to prevent offline download failures.
- Manually trigger native compilation of node-pty via npm rebuild --build-from-source in buildPhase.
- Run stage-native-deps.cjs to copy the natively compiled binary into build/native-deps.
- Flatten native-deps and install-stamp.json to the root of the output derivation in installPhase, matching electron-builder's extraResources behavior so main.cjs can find it at process.resourcesPath + '/native-deps/node-pty'.
- Add doCheck=true and a strict checkPhase to fail fast if the staged native binary is missing.

apps/desktop/electron/main.cjs

@@ -95,6 +95,7 @@ try {
       nodePty = require(nodePtyDir)
     }
   } catch {
+    console.log(`[terminal] failed to load node-pty from path ${nodePtyDir}`)
     nodePty = null
     nodePtyDir = null
   }

apps/desktop/package.json

@@ -18,7 +18,8 @@
     "profile:main": "wait-on http://127.0.0.1:5174 && cross-env XCURSOR_SIZE=24 HERMES_DESKTOP_DEV_SERVER=http://127.0.0.1:5174 electron --inspect=9229 .",
     "profile:main:cpu": "wait-on http://127.0.0.1:5174 && cross-env XCURSOR_SIZE=24 NODE_OPTIONS=--cpu-prof HERMES_DESKTOP_DEV_SERVER=http://127.0.0.1:5174 electron .",
     "start": "npm run build && electron .",
-    "build": "node scripts/assert-root-install.cjs && node scripts/write-build-stamp.cjs && node scripts/stage-native-deps.cjs && tsc -b && vite build && node scripts/assert-dist-built.cjs",
+    "build": "node scripts/assert-root-install.cjs && node scripts/write-build-stamp.cjs && node scripts/stage-native-deps.cjs && tsc -b && vite build && npm run postbuild",
+    "postbuild": "node scripts/assert-dist-built.cjs",
     "builder": "cross-env NODE_OPTIONS=--max-old-space-size=16384 electron-builder",
     "pack": "npm run build && npm run builder -- --dir",
     "dist": "npm run build && npm run builder",