eterm: extract settings actions and fix macOS efsw linkage

Build:
  - Link eterm with CoreFoundation and CoreServices on macOS
  - Satisfy the framework dependencies required by efsw's FSEvents backend

  Applications:
  - Move eterm settings operations into a dedicated SettingsActions class
  - Centralize settings window lifecycle and font configuration actions
  - Route settings panel font-size updates through SettingsActions

premake4.lua

@@ -1943,6 +1943,9 @@ solution "eepp"
 		if os.is_real("linux") then
 			links { "util" }
 		end
+		if os.is("macosx") then
+			links { "CoreFoundation.framework", "CoreServices.framework" }
+		end
 		if os.is("haiku") then
 			links { "bsd" }
 		end