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/doctor/env_check.go

@@ -101,7 +101,7 @@ func (c *EnvVarsCheck) Run(ctx *CheckContext) *CheckResult {
 		}
 
 		// Get expected env vars based on role
-		expected := config.RoleEnvVars(string(identity.Role), identity.Rig, identity.Name)
+		expected := config.AgentEnvSimple(string(identity.Role), identity.Rig, identity.Name)
 
 		// Get actual tmux env vars
 		actual, err := reader.GetAllEnvironment(sess)