Implement SQLite index database layer

- Add pure Go SQLite driver (modernc.org/sqlite) to avoid CGO dependency
- Implement database connection management with WAL mode
- Add write mutex for serializing concurrent writes
- Create schema for all tables matching DESIGN.md specifications
- Implement repository pattern for all database entities:
  - Files, FileChunks, Chunks, Blobs, BlobChunks, ChunkFiles, Snapshots
- Add transaction support with proper rollback handling
- Add fatal error handling for database integrity issues
- Add snapshot fields for tracking file sizes and compression ratios
- Make index path configurable via VAULTIK_INDEX_PATH environment variable
- Add comprehensive test coverage for all repositories
- Add format check to Makefile to ensure code formatting

internal/database/models.go

@@ -57,11 +57,14 @@ type ChunkFile struct {
 
 // Snapshot represents a snapshot record in the database
 type Snapshot struct {
-	ID             string
-	Hostname       string
-	VaultikVersion string
-	CreatedTS      time.Time
-	FileCount      int64
-	ChunkCount     int64
-	BlobCount      int64
+	ID               string
+	Hostname         string
+	VaultikVersion   string
+	CreatedTS        time.Time
+	FileCount        int64
+	ChunkCount       int64
+	BlobCount        int64
+	TotalSize        int64   // Total size of all referenced files
+	BlobSize         int64   // Total size of all referenced blobs (compressed and encrypted)
+	CompressionRatio float64 // Compression ratio (BlobSize / TotalSize)
 }