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/role.go

@@ -506,7 +506,7 @@ func runRoleEnv(cmd *cobra.Command, args []string) error {
 	}
 
 	// Get canonical env vars from shared source of truth
-	envVars := config.RoleEnvVars(string(info.Role), info.Rig, info.Polecat)
+	envVars := config.AgentEnvSimple(string(info.Role), info.Rig, info.Polecat)
 	envVars[EnvGTRoleHome] = home
 
 	// Output in sorted order for consistent output