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/config/viper.go

@@ -0,0 +1,47 @@
+package config
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/spf13/viper"
+)
+
+// NewViper returns a viper instance configured for CODEAGENT_* environment
+// variables and an optional config file.
+//
+// Search order when configFile is empty:
+//   - $HOME/.codeagent/config.(yaml|yml|json|toml|...)
+func NewViper(configFile string) (*viper.Viper, error) {
+	v := viper.New()
+	v.SetEnvPrefix("CODEAGENT")
+	v.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
+	v.AutomaticEnv()
+
+	if strings.TrimSpace(configFile) != "" {
+		v.SetConfigFile(configFile)
+		if err := v.ReadInConfig(); err != nil {
+			return nil, err
+		}
+		return v, nil
+	}
+
+	home, err := os.UserHomeDir()
+	if err != nil || strings.TrimSpace(home) == "" {
+		return v, nil
+	}
+
+	v.SetConfigName("config")
+	v.AddConfigPath(filepath.Join(home, ".codeagent"))
+	if err := v.ReadInConfig(); err != nil {
+		var notFound viper.ConfigFileNotFoundError
+		if errors.As(err, &notFound) {
+			return v, nil
+		}
+		return nil, err
+	}
+
+	return v, nil
+}