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/executor/log_writer_limit_test.go

@@ -0,0 +1,36 @@
+package executor
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestLogWriterWriteLimitsBuffer(t *testing.T) {
+	logger, err := NewLogger()
+	if err != nil {
+		t.Fatalf("NewLogger error: %v", err)
+	}
+	setLogger(logger)
+	t.Cleanup(func() { _ = closeLogger() })
+
+	lw := newLogWriter("P:", 10)
+	_, _ = lw.Write([]byte(strings.Repeat("a", 100)))
+
+	if lw.buf.Len() != 10 {
+		t.Fatalf("logWriter buffer len=%d, want %d", lw.buf.Len(), 10)
+	}
+	if !lw.dropped {
+		t.Fatalf("expected logWriter to drop overlong line bytes")
+	}
+
+	lw.Flush()
+	logger.Flush()
+	data, err := os.ReadFile(logger.Path())
+	if err != nil {
+		t.Fatalf("ReadFile error: %v", err)
+	}
+	if !strings.Contains(string(data), "P:aaaaaaa...") {
+		t.Fatalf("log output missing truncated entry, got %q", string(data))
+	}
+}