fix(doctor): check deacon env vars after AgentEnv refactor

The env-vars doctor check was skipping deacon with a stale comment
"it doesn't use standard env vars". After the AgentEnv refactor,
deacon/manager.go now uses config.AgentEnv() like all other roles.

- Remove the skip condition for deacon in env_check.go
- Update test from TestEnvVarsCheck_DeaconSkipped to test deacon is
  actually checked (TestEnvVarsCheck_DeaconCorrect/DeaconMissing)

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

internal/doctor/env_check.go

@@ -95,11 +95,6 @@ func (c *EnvVarsCheck) Run(ctx *CheckContext) *CheckResult {
 			continue
 		}
 
-		// Skip deacon - it doesn't use the standard env vars
-		if identity.Role == session.RoleDeacon {
-			continue
-		}
-
 		// Get expected env vars based on role
 		expected := config.AgentEnvSimple(string(identity.Role), identity.Rig, identity.Name)