feat: add Windows .exe support

- Add @electron-forge/maker-squirrel for Windows installer
- Create .ico icon from existing PNG
- Fix compositor platform detection for win32
- Forge config now builds both .dmg (macOS) and .exe (Windows)

src/electron/main.ts

@@ -47,7 +47,12 @@ function setupPaths() {
     }
 
     // Compositor binaries (unpacked from asar)
-    const platform = process.platform === 'darwin' ? 'darwin' : 'linux';
+    const platformMap: Record<string, string> = {
+      darwin: 'darwin',
+      win32: 'win32',
+      linux: 'linux',
+    };
+    const platform = platformMap[process.platform] || process.platform;
     const arch = process.arch;
     const compositorPath = path.join(
       resourcesPath,