Add jukebox_maker web app v1.0

Go web application for filling USB drives with media files.
Runs in Docker on Unraid with /media, /mnt/usb, /config volumes.

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

internal/watcher/watcher.go

@@ -0,0 +1,70 @@
+package watcher
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"jukebox_maker/internal/disk"
+)
+
+type DiskEvent struct {
+	Info disk.DiskInfo
+	Prev disk.DiskState
+}
+
+type Handler func(event DiskEvent)
+
+type Watcher struct {
+	mountPath string
+	interval  time.Duration
+	handler   Handler
+
+	mu      sync.RWMutex
+	current disk.DiskInfo
+}
+
+func New(mountPath string, interval time.Duration, handler Handler) *Watcher {
+	return &Watcher{
+		mountPath: mountPath,
+		interval:  interval,
+		handler:   handler,
+	}
+}
+
+func (w *Watcher) CurrentDisk() disk.DiskInfo {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
+	return w.current
+}
+
+func (w *Watcher) Run(ctx context.Context) {
+	ticker := time.NewTicker(w.interval)
+	defer ticker.Stop()
+
+	// probe immediately on start
+	w.probe()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			w.probe()
+		}
+	}
+}
+
+func (w *Watcher) probe() {
+	info, _ := disk.Probe(w.mountPath)
+
+	w.mu.Lock()
+	prev := w.current.State
+	changed := prev != info.State
+	w.current = info
+	w.mu.Unlock()
+
+	if changed && w.handler != nil {
+		w.handler(DiskEvent{Info: info, Prev: prev})
+	}
+}