refactor: restructure codebase to internal/ directory with modular architecture

- Move all source files to internal/{app,backend,config,executor,logger,parser,utils}
- Integrate third-party libraries: zerolog, goccy/go-json, gopsutil, cobra/viper
- Add comprehensive unit tests for utils package (94.3% coverage)
- Add performance benchmarks for string operations
- Fix error display: cleanup warnings no longer pollute Recent Errors
- Add GitHub Actions CI workflow
- Add Makefile for build automation
- Add README documentation

Generated with SWE-Agent.ai

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

codeagent-wrapper/internal/backend/registry.go

@@ -0,0 +1,29 @@
+package backend
+
+import (
+	"fmt"
+	"strings"
+)
+
+var registry = map[string]Backend{
+	"codex":    CodexBackend{},
+	"claude":   ClaudeBackend{},
+	"gemini":   GeminiBackend{},
+	"opencode": OpencodeBackend{},
+}
+
+// Registry exposes the available backends. Intended for internal inspection/tests.
+func Registry() map[string]Backend {
+	return registry
+}
+
+func Select(name string) (Backend, error) {
+	key := strings.ToLower(strings.TrimSpace(name))
+	if key == "" {
+		key = "codex"
+	}
+	if backend, ok := registry[key]; ok {
+		return backend, nil
+	}
+	return nil, fmt.Errorf("unsupported backend %q", name)
+}