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

internal/linux/startup.go

@@ -1,4 +1,12 @@
 //go:build linux
+
+// ============================================================
+// LINUX-ONLY FILE — Linux startup (autostart) management via
+// XDG Desktop Entry files (.desktop). Creates/removes autostart
+// entries and manages the application's .desktop file.
+// The Windows equivalent is in internal/windows/
+// ============================================================
+
 package linux
 
 import (