Add session name helper functions (gt-atqr8)

Create helper functions in internal/session/names.go for consistent
session name construction across Gas Town agents:
- MayorSessionName()
- DeaconSessionName()
- WitnessSessionName(rig)
- RefinerySessionName(rig)
- CrewSessionName(rig, name)
- PolecatSessionName(rig, name)

Includes comprehensive unit tests in names_test.go.

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

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

internal/session/names_test.go

@@ -0,0 +1,104 @@
+package session
+
+import "testing"
+
+func TestMayorSessionName(t *testing.T) {
+	want := "gt-mayor"
+	got := MayorSessionName()
+	if got != want {
+		t.Errorf("MayorSessionName() = %q, want %q", got, want)
+	}
+}
+
+func TestDeaconSessionName(t *testing.T) {
+	want := "gt-deacon"
+	got := DeaconSessionName()
+	if got != want {
+		t.Errorf("DeaconSessionName() = %q, want %q", got, want)
+	}
+}
+
+func TestWitnessSessionName(t *testing.T) {
+	tests := []struct {
+		rig  string
+		want string
+	}{
+		{"gastown", "gt-gastown-witness"},
+		{"beads", "gt-beads-witness"},
+		{"foo", "gt-foo-witness"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.rig, func(t *testing.T) {
+			got := WitnessSessionName(tt.rig)
+			if got != tt.want {
+				t.Errorf("WitnessSessionName(%q) = %q, want %q", tt.rig, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestRefinerySessionName(t *testing.T) {
+	tests := []struct {
+		rig  string
+		want string
+	}{
+		{"gastown", "gt-gastown-refinery"},
+		{"beads", "gt-beads-refinery"},
+		{"foo", "gt-foo-refinery"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.rig, func(t *testing.T) {
+			got := RefinerySessionName(tt.rig)
+			if got != tt.want {
+				t.Errorf("RefinerySessionName(%q) = %q, want %q", tt.rig, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestCrewSessionName(t *testing.T) {
+	tests := []struct {
+		rig  string
+		name string
+		want string
+	}{
+		{"gastown", "max", "gt-gastown-crew-max"},
+		{"beads", "alice", "gt-beads-crew-alice"},
+		{"foo", "bar", "gt-foo-crew-bar"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.rig+"/"+tt.name, func(t *testing.T) {
+			got := CrewSessionName(tt.rig, tt.name)
+			if got != tt.want {
+				t.Errorf("CrewSessionName(%q, %q) = %q, want %q", tt.rig, tt.name, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestPolecatSessionName(t *testing.T) {
+	tests := []struct {
+		rig  string
+		name string
+		want string
+	}{
+		{"gastown", "Toast", "gt-gastown-Toast"},
+		{"gastown", "Furiosa", "gt-gastown-Furiosa"},
+		{"beads", "worker1", "gt-beads-worker1"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.rig+"/"+tt.name, func(t *testing.T) {
+			got := PolecatSessionName(tt.rig, tt.name)
+			if got != tt.want {
+				t.Errorf("PolecatSessionName(%q, %q) = %q, want %q", tt.rig, tt.name, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestPrefix(t *testing.T) {
+	want := "gt-"
+	if Prefix != want {
+		t.Errorf("Prefix = %q, want %q", Prefix, want)
+	}
+}