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)

extract_test.go

@@ -368,3 +368,116 @@ func TestRunExtraction_CreatesVolumeDirs(t *testing.T) {
 		t.Error("expected lcd / to be in commands")
 	}
 }
+
+func TestParseTags(t *testing.T) {
+	t.Run("parses basic tag list", func(t *testing.T) {
+		out := `
+tag  name
+-----------------
+ 01  Drums
+ 02  Bass
+ 03  FX
+ 04  Vox
+ 05  Percussion
+-----------------
+`
+		tags := parseTags(out)
+		if len(tags) != 5 {
+			t.Fatalf("expected 5 tags, got %d", len(tags))
+		}
+		if tags[0].Index != 1 || tags[0].Name != "Drums" {
+			t.Errorf("tag 0: got {%d %s}, want {1 Drums}", tags[0].Index, tags[0].Name)
+		}
+		if tags[4].Index != 5 || tags[4].Name != "Percussion" {
+			t.Errorf("tag 4: got {%d %s}, want {5 Percussion}", tags[4].Index, tags[4].Name)
+		}
+	})
+
+	t.Run("parses tags with spaces in names", func(t *testing.T) {
+		out := `
+tag  name
+-----------------
+ 01  Kick Drum
+ 02  Hi Hat
+ 03  Snare Drum
+-----------------
+`
+		tags := parseTags(out)
+		if len(tags) != 3 {
+			t.Fatalf("expected 3 tags, got %d", len(tags))
+		}
+		if tags[0].Name != "Kick Drum" {
+			t.Errorf("got %q, want 'Kick Drum'", tags[0].Name)
+		}
+	})
+
+	t.Run("handles default tag names from akaiutil", func(t *testing.T) {
+		out := `
+tag  name
+-----------------
+ 01  TAG A
+ 02  TAG B
+ 03  MyTag
+-----------------
+`
+		tags := parseTags(out)
+		if len(tags) != 3 {
+			t.Fatalf("expected 3 tags, got %d", len(tags))
+		}
+	})
+
+	t.Run("no tags present message returns empty", func(t *testing.T) {
+		out := "no tags present\n"
+		tags := parseTags(out)
+		if len(tags) != 0 {
+			t.Errorf("expected 0 tags, got %d", len(tags))
+		}
+	})
+
+	t.Run("handles empty output", func(t *testing.T) {
+		tags := parseTags("")
+		if len(tags) != 0 {
+			t.Errorf("expected 0 tags, got %d", len(tags))
+		}
+	})
+
+	t.Run("handles no tags in partition type", func(t *testing.T) {
+		out := "no tags in this partition type\n"
+		tags := parseTags(out)
+		if len(tags) != 0 {
+			t.Errorf("expected 0 tags, got %d", len(tags))
+		}
+	})
+}
+
+func TestListTags_Integration(t *testing.T) {
+	origRun := runAkaiutil
+	defer func() { runAkaiutil = origRun }()
+
+	runAkaiutil = func(isoPath, commands string) (string, error) {
+		return `
+/disk0/A > lstags
+
+tag  name
+-----------------
+ 01  Drums
+ 02  Bass
+ 03  FX
+-----------------
+		`, nil
+	}
+
+	tags, err := listTags("fake.iso", "A", "SomeVolume")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(tags) != 3 {
+		t.Errorf("expected 3 tags, got %d", len(tags))
+	}
+	if tags[0].Name != "Drums" {
+		t.Errorf("expected Drums, got %s", tags[0].Name)
+	}
+	if tags[2].Index != 3 || tags[2].Name != "FX" {
+		t.Errorf("tag 2: got {%d %s}, want {3 FX}", tags[2].Index, tags[2].Name)
+	}
+}