Add tests and multi-platform keybind support (Linux, macOS, Windows)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

main.go

@@ -21,9 +21,12 @@ type Config struct {
 	ExemptUsers []string `json:"exempt_users"`
 }
 
-func loadConfig() (*Config, error) {
-	exe, _ := os.Executable()
-	for _, dir := range []string{filepath.Dir(exe), "."} {
+func loadConfig(dirs ...string) (*Config, error) {
+	if len(dirs) == 0 {
+		exe, _ := os.Executable()
+		dirs = []string{filepath.Dir(exe), "."}
+	}
+	for _, dir := range dirs {
 		data, err := os.ReadFile(filepath.Join(dir, "config.json"))
 		if err != nil {
 			continue
@@ -37,14 +40,6 @@ func loadConfig() (*Config, error) {
 	return nil, fmt.Errorf("config.json not found next to executable or in working directory")
 }
 
-var modMap = map[string]hotkey.Modifier{
-	"ctrl":  hotkey.ModCtrl,
-	"shift": hotkey.ModShift,
-	"alt":   hotkey.ModAlt,
-	"win":   hotkey.ModWin,
-	"super": hotkey.ModWin,
-}
-
 var keyMap = map[string]hotkey.Key{
 	"a": hotkey.KeyA, "b": hotkey.KeyB, "c": hotkey.KeyC, "d": hotkey.KeyD,
 	"e": hotkey.KeyE, "f": hotkey.KeyF, "g": hotkey.KeyG, "h": hotkey.KeyH,