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/api/handlers_sources.go

@@ -0,0 +1,26 @@
+package api
+
+import (
+	"net/http"
+	"os"
+)
+
+func (s *Server) handleSources(w http.ResponseWriter, r *http.Request) {
+	entries, err := os.ReadDir(s.deps.MediaPath)
+	if err != nil {
+		jsonOK(w, map[string][]string{"items": {}})
+		return
+	}
+
+	var items []string
+	for _, e := range entries {
+		if e.IsDir() && e.Name()[0] != '.' {
+			items = append(items, e.Name())
+		}
+	}
+	if items == nil {
+		items = []string{}
+	}
+
+	jsonOK(w, map[string][]string{"items": items})
+}