feat: Set BD_ACTOR env var when spawning agents (gt-rhfji)

When gt spawns agents (polecats, crew, patrol roles), it now sets the
BD_ACTOR env var so that bd commands (like `bd hook`) know the agent
identity without coupling to gt.

Updated spawn points:
- gt up (mayor, deacon, witness via ensureSession/ensureWitness)
- gt deacon start
- gt witness start
- gt start refinery
- gt mayor start
- Daemon deacon restart
- Daemon lifecycle restart
- Handoff respawn
- Refinery manager start

BD_ACTOR uses slash format (e.g., gastown/witness, gastown/crew/max)
while GT_ROLE may use dash format internally.

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

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

internal/refinery/manager.go

@@ -200,9 +200,11 @@ func (m *Manager) Start(foreground bool) error {
 	}
 
 	// Set environment variables
+	bdActor := fmt.Sprintf("%s/refinery", m.rig.Name)
 	_ = t.SetEnvironment(sessionID, "GT_RIG", m.rig.Name)
 	_ = t.SetEnvironment(sessionID, "GT_REFINERY", "1")
 	_ = t.SetEnvironment(sessionID, "GT_ROLE", "refinery")
+	_ = t.SetEnvironment(sessionID, "BD_ACTOR", bdActor)
 
 	// Set beads environment - refinery uses rig-level beads
 	beadsDir := filepath.Join(m.rig.Path, "mayor", "rig", ".beads")