feat: Sample Tag Viewer — read-only tag browser for AKAI disk images

Backend:
- extract.go: listTags() navigates to volume, runs akaiutil lstags
- extract.go: parseTags() parses tag name/index from lstags output
- serve.go: GET /api/disk/partitions — list partitions on an ISO
- serve.go: GET /api/disk/volumes — list volumes on a partition
- serve.go: GET /api/volume/tags — list tags on a volume

Web UI:
- Tag Viewer section with ISO path input and Browse button
- Partition selector buttons
- Volume grid with click-to-select
- Tag chips with color-coded dots (20-color palette)

Tests:
- 6 parseTags tests (basic, spaces, defaults, no tags, empty, no-type)
- 1 listTags integration test
- 4 API endpoint tests (partitions, missing-ISO, missing-params, tags)

Karpathy: read-only view first — no write operations yet (settagi, clrtagi)

serve.go

@@ -55,6 +55,9 @@ func cmdServe(args []string) {
 	mux.HandleFunc("/api/search", handleSearch)
 	mux.HandleFunc("/api/list", handleList)
 	mux.HandleFunc("/api/list-wavs", handleListWavs)
+	mux.HandleFunc("/api/disk/partitions", handleDiskPartitions)
+	mux.HandleFunc("/api/disk/volumes", handleDiskVolumes)
+	mux.HandleFunc("/api/volume/tags", handleVolumeTags)
 	mux.HandleFunc("/api/download", handleAPIDownload)
 	mux.HandleFunc("/api/extract", handleAPIExtract)
 	mux.HandleFunc("/api/progress", handleProgress)
@@ -300,6 +303,63 @@ func handleListWavs(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, files)
 }
 
+func handleDiskPartitions(w http.ResponseWriter, r *http.Request) {
+	iso := r.URL.Query().Get("iso")
+	if iso == "" {
+		writeJSON(w, map[string]any{"error": "missing iso parameter"})
+		return
+	}
+	parts, err := listPartitions(iso)
+	if err != nil {
+		writeJSON(w, map[string]any{"error": err.Error()})
+		return
+	}
+	writeJSON(w, parts)
+}
+
+func handleDiskVolumes(w http.ResponseWriter, r *http.Request) {
+	iso := r.URL.Query().Get("iso")
+	part := r.URL.Query().Get("part")
+	if iso == "" || part == "" {
+		writeJSON(w, map[string]any{"error": "missing iso or part parameter"})
+		return
+	}
+	parts, err := listPartitions(iso)
+	if err != nil {
+		writeJSON(w, map[string]any{"error": err.Error()})
+		return
+	}
+	vols, err := listVolumes(iso, parts)
+	if err != nil {
+		writeJSON(w, map[string]any{"error": err.Error()})
+		return
+	}
+	var filtered []volInfo
+	for _, v := range vols {
+		if v.Part == part {
+			filtered = append(filtered, v)
+		}
+	}
+	writeJSON(w, filtered)
+}
+
+func handleVolumeTags(w http.ResponseWriter, r *http.Request) {
+	iso := r.URL.Query().Get("iso")
+	part := r.URL.Query().Get("part")
+	vol := r.URL.Query().Get("vol")
+	if iso == "" || part == "" || vol == "" {
+		writeJSON(w, map[string]any{"error": "missing iso, part, or vol parameter"})
+		return
+	}
+
+	tags, err := listTags(iso, part, vol)
+	if err != nil {
+		writeJSON(w, map[string]any{"error": err.Error()})
+		return
+	}
+	writeJSON(w, tags)
+}
+
 func handleProgress(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "text/event-stream")
 	w.Header().Set("Cache-Control", "no-cache")