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

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

codeagent-wrapper/internal/app/terminal_test.go

@@ -0,0 +1,30 @@
+package wrapper
+
+import (
+	"os"
+	"testing"
+)
+
+func TestDefaultIsTerminalCoverage(t *testing.T) {
+	oldStdin := os.Stdin
+	t.Cleanup(func() { os.Stdin = oldStdin })
+
+	f, err := os.CreateTemp(t.TempDir(), "stdin-*")
+	if err != nil {
+		t.Fatalf("os.CreateTemp() error = %v", err)
+	}
+	defer os.Remove(f.Name())
+
+	os.Stdin = f
+	if got := defaultIsTerminal(); got {
+		t.Fatalf("defaultIsTerminal() = %v, want false for regular file", got)
+	}
+
+	if err := f.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	os.Stdin = f
+	if got := defaultIsTerminal(); !got {
+		t.Fatalf("defaultIsTerminal() = %v, want true when Stat fails", got)
+	}
+}