Replace logging system with slog and tint for structured colored output

- Add logger.go with public Logger variable and InitLogger function
- Replace all fmt.Printf/fmt.Fprintf calls with structured Logger.Info/Logger.Error
- Initialize logger in main function for consistent access across packages
- Keep fmt.Errorf for proper error creation (standard Go practice)
- Add tint dependency for colorized terminal output with timestamps
- Convert user output to structured logging with key-value pairs
- Update info command to use structured logging for plugin details
- Update updateassets command to use structured progress logging
- Update version command to use structured logging
- Update authentication logging in client.go with structured fields
- Update enable/disable commands to use structured logging
- Remove unused fmt imports after conversion

All output now uses slog with tint for beautiful, structured, colorized logging
while maintaining proper error handling with fmt.Errorf for error creation.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

logger.go

@@ -0,0 +1,37 @@
+package pluginctl
+
+import (
+	"log/slog"
+	"os"
+	"time"
+
+	"github.com/lmittmann/tint"
+)
+
+// Logger is the global logger instance
+var Logger *slog.Logger
+
+// InitLogger initializes the global logger
+func InitLogger() {
+	// Create a tint handler for colorized output
+	handler := tint.NewHandler(os.Stderr, &tint.Options{
+		Level:      slog.LevelInfo,
+		TimeFormat: time.Kitchen,
+		AddSource:  false,
+		NoColor:    false,
+	})
+
+	Logger = slog.New(handler)
+}
+
+// SetLogLevel sets the minimum logging level
+func SetLogLevel(level slog.Level) {
+	handler := tint.NewHandler(os.Stderr, &tint.Options{
+		Level:      level,
+		TimeFormat: time.Kitchen,
+		AddSource:  false,
+		NoColor:    false,
+	})
+
+	Logger = slog.New(handler)
+}