fix: use ANTHROPIC_AUTH_TOKEN for Claude CLI env injection

- Change env var from ANTHROPIC_API_KEY to ANTHROPIC_AUTH_TOKEN
- Add Backend field propagation in taskSpec (cli.go)
- Add stderr logging for injected env vars with API key masking
- Add comprehensive tests for env injection flow

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

codeagent-wrapper/internal/app/cli.go

@@ -635,6 +635,7 @@ func runSingleMode(cfg *Config, name string) int {
 		WorkDir:         cfg.WorkDir,
 		Mode:            cfg.Mode,
 		SessionID:       cfg.SessionID,
+		Backend:         cfg.Backend,
 		Model:           cfg.Model,
 		ReasoningEffort: cfg.ReasoningEffort,
 		Agent:           cfg.Agent,