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.go

@@ -0,0 +1,37 @@
+// Package session provides polecat session lifecycle management.
+package session
+
+import "fmt"
+
+// Prefix is the common prefix for all Gas Town tmux session names.
+const Prefix = "gt-"
+
+// MayorSessionName returns the session name for the Mayor agent.
+func MayorSessionName() string {
+	return Prefix + "mayor"
+}
+
+// DeaconSessionName returns the session name for the Deacon agent.
+func DeaconSessionName() string {
+	return Prefix + "deacon"
+}
+
+// WitnessSessionName returns the session name for a rig's Witness agent.
+func WitnessSessionName(rig string) string {
+	return fmt.Sprintf("%s%s-witness", Prefix, rig)
+}
+
+// RefinerySessionName returns the session name for a rig's Refinery agent.
+func RefinerySessionName(rig string) string {
+	return fmt.Sprintf("%s%s-refinery", Prefix, rig)
+}
+
+// CrewSessionName returns the session name for a crew worker in a rig.
+func CrewSessionName(rig, name string) string {
+	return fmt.Sprintf("%s%s-crew-%s", Prefix, rig, name)
+}
+
+// PolecatSessionName returns the session name for a polecat in a rig.
+func PolecatSessionName(rig, name string) string {
+	return fmt.Sprintf("%s%s-%s", Prefix, rig, name)
+}