[client/ui] Enable tray status row on Linux to avoid greyed-out indicator

The informational status row at the top of the tray menu was disabled on
Linux, which painted the connection-status indicator greyed-out. Enable
it on Linux so the row renders at full opacity; it has no OnClick handler
so clicking it remains a no-op.

client/ui/tray_status_enabled_linux.go

@@ -0,0 +1,14 @@
+//go:build linux
+
+package main
+
+// statusRowEnabled reports whether the informational status row at the
+// top of the tray menu should stay enabled. True on Linux: a disabled
+// row is painted greyed-out, which makes the connection-status indicator
+// at the top of the menu look washed-out. Keeping it enabled lets the
+// row (and its coloured status dot) render at full opacity. The row has
+// no OnClick handler, so clicking it is still a no-op — enabling only
+// affects how it is drawn, not its behaviour. macOS disables the row
+// (tray_status_enabled_other.go); Windows enables it for a different
+// reason (tray_status_enabled_windows.go).
+func statusRowEnabled() bool { return true }