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_test.go

@@ -544,4 +544,93 @@ func TestHandleListWavs_NonExistentDir(t *testing.T) {
 	if _, ok := resp["error"]; !ok {
 		t.Error("expected error for nonexistent dir")
 	}
+}
+
+func TestHandleDiskPartitions_ReturnsPartitions(t *testing.T) {
+	origRun := runAkaiutil
+	defer func() { runAkaiutil = origRun }()
+
+	runAkaiutil = func(isoPath, commands string) (string, error) {
+		return `
+Disk /disk0
+Total blocks: 0 (0 KB each) 0 KB
+Partition table:
+  A - S1000 HD (0 blocks)
+  B - S1000 HD (0 blocks)
+		`, nil
+	}
+
+	req := httptest.NewRequest("GET", "/api/disk/partitions?iso=test.iso", nil)
+	rr := httptest.NewRecorder()
+	handleDiskPartitions(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", rr.Code)
+	}
+	var parts []string
+	if err := json.Unmarshal(rr.Body.Bytes(), &parts); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+	if len(parts) != 2 {
+		t.Errorf("expected 2 partitions, got %d: %v", len(parts), parts)
+	}
+}
+
+func TestHandleDiskPartitions_MissingISO(t *testing.T) {
+	req := httptest.NewRequest("GET", "/api/disk/partitions", nil)
+	rr := httptest.NewRecorder()
+	handleDiskPartitions(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", rr.Code)
+	}
+	var resp map[string]any
+	_ = json.Unmarshal(rr.Body.Bytes(), &resp)
+	if _, ok := resp["error"]; !ok {
+		t.Error("expected error for missing iso")
+	}
+}
+
+func TestHandleVolumeTags_MissingParams(t *testing.T) {
+	req := httptest.NewRequest("GET", "/api/volume/tags", nil)
+	rr := httptest.NewRecorder()
+	handleVolumeTags(rr, req)
+
+	var resp map[string]any
+	_ = json.Unmarshal(rr.Body.Bytes(), &resp)
+	if resp["error"] == nil {
+		t.Error("expected error for missing params")
+	}
+}
+
+func TestHandleVolumeTags_ReturnsTags(t *testing.T) {
+	origRun := runAkaiutil
+	defer func() { runAkaiutil = origRun }()
+
+	runAkaiutil = func(isoPath, commands string) (string, error) {
+		return `
+/disk0/A/SomeVol > lstags
+
+tag  name
+-----------------
+ 01  Drums
+ 02  Bass
+-----------------
+		`, nil
+	}
+
+	req := httptest.NewRequest("GET", "/api/volume/tags?iso=test.iso&part=A&vol=SomeVol", nil)
+	rr := httptest.NewRecorder()
+	handleVolumeTags(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", rr.Code)
+	}
+	var tags []TagInfo
+	if err := json.Unmarshal(rr.Body.Bytes(), &tags); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+	if len(tags) != 2 {
+		t.Errorf("expected 2 tags, got %d", len(tags))
+	}
 }