refactor: extract storage system to storage package

Extracted BadgerDB operations, compression, and revision management
from main.go to dedicated storage package for better modularity.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

storage/compression.go

@@ -0,0 +1,60 @@
+package storage
+
+import (
+	"fmt"
+	
+	"github.com/klauspost/compress/zstd"
+)
+
+// CompressionService handles ZSTD compression and decompression
+type CompressionService struct {
+	compressor   *zstd.Encoder
+	decompressor *zstd.Decoder
+}
+
+// NewCompressionService creates a new compression service
+func NewCompressionService() (*CompressionService, error) {
+	// Initialize ZSTD compressor
+	compressor, err := zstd.NewWriter(nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to initialize ZSTD compressor: %v", err)
+	}
+
+	// Initialize ZSTD decompressor
+	decompressor, err := zstd.NewReader(nil)
+	if err != nil {
+		compressor.Close()
+		return nil, fmt.Errorf("failed to initialize ZSTD decompressor: %v", err)
+	}
+
+	return &CompressionService{
+		compressor:   compressor,
+		decompressor: decompressor,
+	}, nil
+}
+
+// Close closes the compression and decompression resources
+func (c *CompressionService) Close() {
+	if c.compressor != nil {
+		c.compressor.Close()
+	}
+	if c.decompressor != nil {
+		c.decompressor.Close()
+	}
+}
+
+// CompressData compresses data using ZSTD
+func (c *CompressionService) CompressData(data []byte) ([]byte, error) {
+	if c.compressor == nil {
+		return nil, fmt.Errorf("compressor not initialized")
+	}
+	return c.compressor.EncodeAll(data, make([]byte, 0, len(data))), nil
+}
+
+// DecompressData decompresses ZSTD-compressed data
+func (c *CompressionService) DecompressData(compressedData []byte) ([]byte, error) {
+	if c.decompressor == nil {
+		return nil, fmt.Errorf("decompressor not initialized")
+	}
+	return c.decompressor.DecodeAll(compressedData, nil)
+}