Implement local SQLite index database with repositories

- Add SQLite database connection management with proper error handling
- Implement schema for files, chunks, blobs, and snapshots tables
- Create repository pattern for each database table
- Add transaction support with proper rollback handling
- Integrate database module with fx dependency injection
- Make index path configurable via VAULTIK_INDEX_PATH env var
- Add fatal error handling for database integrity issues
- Update DESIGN.md to clarify file_chunks vs chunk_files distinction
- Remove FinalHash from BlobInfo (blobs are content-addressable)
- Add file metadata support (mtime, ctime, mode, uid, gid, symlinks)

internal/database/blob_chunks.go

@@ -0,0 +1,88 @@
+package database
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+type BlobChunkRepository struct {
+	db *DB
+}
+
+func NewBlobChunkRepository(db *DB) *BlobChunkRepository {
+	return &BlobChunkRepository{db: db}
+}
+
+func (r *BlobChunkRepository) Create(ctx context.Context, tx *sql.Tx, bc *BlobChunk) error {
+	query := `
+		INSERT INTO blob_chunks (blob_hash, chunk_hash, offset, length)
+		VALUES (?, ?, ?, ?)
+	`
+
+	var err error
+	if tx != nil {
+		_, err = tx.ExecContext(ctx, query, bc.BlobHash, bc.ChunkHash, bc.Offset, bc.Length)
+	} else {
+		_, err = r.db.conn.ExecContext(ctx, query, bc.BlobHash, bc.ChunkHash, bc.Offset, bc.Length)
+	}
+
+	if err != nil {
+		return fmt.Errorf("inserting blob_chunk: %w", err)
+	}
+
+	return nil
+}
+
+func (r *BlobChunkRepository) GetByBlobHash(ctx context.Context, blobHash string) ([]*BlobChunk, error) {
+	query := `
+		SELECT blob_hash, chunk_hash, offset, length
+		FROM blob_chunks
+		WHERE blob_hash = ?
+		ORDER BY offset
+	`
+
+	rows, err := r.db.conn.QueryContext(ctx, query, blobHash)
+	if err != nil {
+		return nil, fmt.Errorf("querying blob chunks: %w", err)
+	}
+	defer CloseRows(rows)
+
+	var blobChunks []*BlobChunk
+	for rows.Next() {
+		var bc BlobChunk
+		err := rows.Scan(&bc.BlobHash, &bc.ChunkHash, &bc.Offset, &bc.Length)
+		if err != nil {
+			return nil, fmt.Errorf("scanning blob chunk: %w", err)
+		}
+		blobChunks = append(blobChunks, &bc)
+	}
+
+	return blobChunks, rows.Err()
+}
+
+func (r *BlobChunkRepository) GetByChunkHash(ctx context.Context, chunkHash string) (*BlobChunk, error) {
+	query := `
+		SELECT blob_hash, chunk_hash, offset, length
+		FROM blob_chunks
+		WHERE chunk_hash = ?
+		LIMIT 1
+	`
+
+	var bc BlobChunk
+	err := r.db.conn.QueryRowContext(ctx, query, chunkHash).Scan(
+		&bc.BlobHash,
+		&bc.ChunkHash,
+		&bc.Offset,
+		&bc.Length,
+	)
+
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("querying blob chunk: %w", err)
+	}
+
+	return &bc, nil
+}