Add automatic log rotation for daemon (bd-154)

- Integrated lumberjack library for production-ready log rotation
- Configurable via env vars: BEADS_DAEMON_LOG_MAX_SIZE, BEADS_DAEMON_LOG_MAX_BACKUPS, BEADS_DAEMON_LOG_MAX_AGE, BEADS_DAEMON_LOG_COMPRESS
- Defaults: 10MB max size, 3 backups, 7 day retention, compression enabled
- Added comprehensive tests for env var parsing and rotation config
- Updated README.md and CHANGELOG.md with rotation documentation
- Prevents unbounded log growth for long-running daemons

Amp-Thread-ID: https://ampcode.com/threads/T-8232d41a-6872-4f4c-962c-7fae8f5e83b7
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/daemon_rotation_test.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestLogRotation(t *testing.T) {
+	
+	// Set small max size for testing (1 MB)
+	os.Setenv("BEADS_DAEMON_LOG_MAX_SIZE", "1")
+	os.Setenv("BEADS_DAEMON_LOG_MAX_BACKUPS", "2")
+	os.Setenv("BEADS_DAEMON_LOG_MAX_AGE", "7")
+	os.Setenv("BEADS_DAEMON_LOG_COMPRESS", "false") // disable for easier testing
+	defer func() {
+		os.Unsetenv("BEADS_DAEMON_LOG_MAX_SIZE")
+		os.Unsetenv("BEADS_DAEMON_LOG_MAX_BACKUPS")
+		os.Unsetenv("BEADS_DAEMON_LOG_MAX_AGE")
+		os.Unsetenv("BEADS_DAEMON_LOG_COMPRESS")
+	}()
+	
+	// Test env parsing
+	maxSize := getEnvInt("BEADS_DAEMON_LOG_MAX_SIZE", 10)
+	if maxSize != 1 {
+		t.Errorf("Expected max size 1, got %d", maxSize)
+	}
+	
+	maxBackups := getEnvInt("BEADS_DAEMON_LOG_MAX_BACKUPS", 3)
+	if maxBackups != 2 {
+		t.Errorf("Expected max backups 2, got %d", maxBackups)
+	}
+	
+	compress := getEnvBool("BEADS_DAEMON_LOG_COMPRESS", true)
+	if compress {
+		t.Errorf("Expected compress false, got true")
+	}
+}
+
+func TestGetEnvInt(t *testing.T) {
+	tests := []struct {
+		name         string
+		envValue     string
+		defaultValue int
+		expected     int
+	}{
+		{"not set", "", 10, 10},
+		{"valid int", "42", 10, 42},
+		{"invalid int", "invalid", 10, 10},
+		{"zero", "0", 10, 0},
+		{"negative", "-5", 10, -5},
+	}
+	
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.envValue != "" {
+				os.Setenv("TEST_INT", tt.envValue)
+				defer os.Unsetenv("TEST_INT")
+			} else {
+				os.Unsetenv("TEST_INT")
+			}
+			
+			result := getEnvInt("TEST_INT", tt.defaultValue)
+			if result != tt.expected {
+				t.Errorf("Expected %d, got %d", tt.expected, result)
+			}
+		})
+	}
+}
+
+func TestGetEnvBool(t *testing.T) {
+	tests := []struct {
+		name         string
+		envValue     string
+		defaultValue bool
+		expected     bool
+	}{
+		{"not set default true", "", true, true},
+		{"not set default false", "", false, false},
+		{"true string", "true", false, true},
+		{"1 string", "1", false, true},
+		{"false string", "false", true, false},
+		{"0 string", "0", true, false},
+		{"invalid string", "invalid", true, false},
+	}
+	
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.envValue != "" {
+				os.Setenv("TEST_BOOL", tt.envValue)
+				defer os.Unsetenv("TEST_BOOL")
+			} else {
+				os.Unsetenv("TEST_BOOL")
+			}
+			
+			result := getEnvBool("TEST_BOOL", tt.defaultValue)
+			if result != tt.expected {
+				t.Errorf("Expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}
+
+func TestLogFileRotationDefaults(t *testing.T) {
+	// Test default values when no env vars set
+	os.Unsetenv("BEADS_DAEMON_LOG_MAX_SIZE")
+	os.Unsetenv("BEADS_DAEMON_LOG_MAX_BACKUPS")
+	os.Unsetenv("BEADS_DAEMON_LOG_MAX_AGE")
+	os.Unsetenv("BEADS_DAEMON_LOG_COMPRESS")
+	
+	maxSize := getEnvInt("BEADS_DAEMON_LOG_MAX_SIZE", 10)
+	if maxSize != 10 {
+		t.Errorf("Expected default max size 10, got %d", maxSize)
+	}
+	
+	maxBackups := getEnvInt("BEADS_DAEMON_LOG_MAX_BACKUPS", 3)
+	if maxBackups != 3 {
+		t.Errorf("Expected default max backups 3, got %d", maxBackups)
+	}
+	
+	maxAge := getEnvInt("BEADS_DAEMON_LOG_MAX_AGE", 7)
+	if maxAge != 7 {
+		t.Errorf("Expected default max age 7, got %d", maxAge)
+	}
+	
+	compress := getEnvBool("BEADS_DAEMON_LOG_COMPRESS", true)
+	if !compress {
+		t.Errorf("Expected default compress true, got false")
+	}
+}