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/cmd/deacon.go

@@ -358,8 +358,15 @@ func startDeaconSession(t *tmux.Tmux, sessionName, agentOverride string) error {
 	}
 
 	// Set environment (non-fatal: session works without these)
-	_ = t.SetEnvironment(sessionName, "GT_ROLE", "deacon")
-	_ = t.SetEnvironment(sessionName, "BD_ACTOR", "deacon")
+	// Use centralized AgentEnv for consistency across all role startup paths
+	envVars := config.AgentEnv(config.AgentEnvConfig{
+		Role:     "deacon",
+		TownRoot: townRoot,
+		BeadsDir: beads.ResolveBeadsDir(townRoot),
+	})
+	for k, v := range envVars {
+		_ = t.SetEnvironment(sessionName, k, v)
+	}
 
 	// Apply Deacon theme (non-fatal: theming failure doesn't affect operation)
 	// Note: ConfigureGasTownSession includes cycle bindings