fix: Add cross-platform handling for tray, updater, and icon generation

- Add platform notes for tray startup, shortcut saving, and Linux-only settings
- Handle stat error in processRecording (missing file)
- Select correct binary name based on OS in updater
- Increase tray icon canvas size from 64 to 128 pixels
- Update frontend dist asset hash

main_instance_stub.go

@@ -1,5 +1,12 @@
 //go:build windows
 
+// ============================================================
+// WINDOWS-ONLY FILE — Stub for the Unix domain socket IPC.
+// On Windows, single-instance enforcement uses a lock file
+// (see main.go), and helper invocations don't use Unix sockets.
+// The real Unix implementation is in main_instance_unix.go
+// ============================================================
+
 package main
 
 // secondInstanceWake is unused on Windows (second-instance UX not wired here).