refactor: consolidate agent env vars into config.AgentEnv

Create centralized AgentEnv function as single source of truth for all
agent environment variables. All agents now consistently receive:
- GT_ROLE, BD_ACTOR, GIT_AUTHOR_NAME (role identity)
- GT_ROOT, BEADS_DIR (workspace paths)
- GT_RIG, GT_POLECAT/GT_CREW (rig-specific identity)
- BEADS_AGENT_NAME, BEADS_NO_DAEMON (beads config)
- CLAUDE_CONFIG_DIR (optional account selection)

Remove RoleEnvVars in favor of AgentEnvSimple wrapper.
Remove IncludeBeadsEnv flag - beads env vars always included.
Update all manager and cmd call sites to use AgentEnv.

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

internal/boot/boot.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"time"
 
+	"github.com/steveyegge/gastown/internal/beads"
 	"github.com/steveyegge/gastown/internal/config"
 	"github.com/steveyegge/gastown/internal/tmux"
 )
@@ -190,9 +191,15 @@ func (b *Boot) spawnTmux() error {
 		return fmt.Errorf("creating boot session: %w", err)
 	}
 
-	// Set environment
-	_ = b.tmux.SetEnvironment(SessionName, "GT_ROLE", "boot")
-	_ = b.tmux.SetEnvironment(SessionName, "BD_ACTOR", "deacon-boot")
+	// Set environment using centralized AgentEnv for consistency
+	envVars := config.AgentEnv(config.AgentEnvConfig{
+		Role:     "boot",
+		TownRoot: b.townRoot,
+		BeadsDir: beads.ResolveBeadsDir(b.townRoot),
+	})
+	for k, v := range envVars {
+		_ = b.tmux.SetEnvironment(SessionName, k, v)
+	}
 
 	// Launch Claude with environment exported inline and initial triage prompt
 	// The "gt boot triage" prompt tells Boot to immediately start triage (GUPP principle)