Add polecat session cycling (C-b n/p)

Polecats for a rig now cycle among themselves, like crew members.
Session groups are now:
- Town: Mayor ↔ Deacon
- Crew: All crew in same rig
- Rig infra: Witness ↔ Refinery
- Polecats: All polecats in same rig

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/polecat_cycle_test.go

@@ -0,0 +1,118 @@
+package cmd
+
+import "testing"
+
+func TestParsePolecatSessionName(t *testing.T) {
+	tests := []struct {
+		name        string
+		sessionName string
+		wantRig     string
+		wantPolecat string
+		wantOk      bool
+	}{
+		// Valid polecat sessions
+		{
+			name:        "simple polecat",
+			sessionName: "gt-gastown-Toast",
+			wantRig:     "gastown",
+			wantPolecat: "Toast",
+			wantOk:      true,
+		},
+		{
+			name:        "another polecat",
+			sessionName: "gt-gastown-Nux",
+			wantRig:     "gastown",
+			wantPolecat: "Nux",
+			wantOk:      true,
+		},
+		{
+			name:        "polecat in different rig",
+			sessionName: "gt-beads-Worker",
+			wantRig:     "beads",
+			wantPolecat: "Worker",
+			wantOk:      true,
+		},
+		{
+			name:        "polecat with hyphen in name",
+			sessionName: "gt-gastown-Max-01",
+			wantRig:     "gastown",
+			wantPolecat: "Max-01",
+			wantOk:      true,
+		},
+
+		// Not polecat sessions (should return false)
+		{
+			name:        "crew session",
+			sessionName: "gt-gastown-crew-jack",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "witness session",
+			sessionName: "gt-gastown-witness",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "refinery session",
+			sessionName: "gt-gastown-refinery",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "mayor session",
+			sessionName: "gt-mayor",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "deacon session",
+			sessionName: "gt-deacon",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "no gt prefix",
+			sessionName: "gastown-Toast",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "empty string",
+			sessionName: "",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "just gt prefix",
+			sessionName: "gt-",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+		{
+			name:        "no name after rig",
+			sessionName: "gt-gastown-",
+			wantRig:     "",
+			wantPolecat: "",
+			wantOk:      false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotRig, gotPolecat, gotOk := parsePolecatSessionName(tt.sessionName)
+			if gotRig != tt.wantRig || gotPolecat != tt.wantPolecat || gotOk != tt.wantOk {
+				t.Errorf("parsePolecatSessionName(%q) = (%q, %q, %v), want (%q, %q, %v)",
+					tt.sessionName, gotRig, gotPolecat, gotOk, tt.wantRig, tt.wantPolecat, tt.wantOk)
+			}
+		})
+	}
+}