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/blobs.go

@@ -0,0 +1,96 @@
+package database
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+)
+
+type BlobRepository struct {
+	db *DB
+}
+
+func NewBlobRepository(db *DB) *BlobRepository {
+	return &BlobRepository{db: db}
+}
+
+func (r *BlobRepository) Create(ctx context.Context, tx *sql.Tx, blob *Blob) error {
+	query := `
+		INSERT INTO blobs (blob_hash, created_ts)
+		VALUES (?, ?)
+	`
+
+	var err error
+	if tx != nil {
+		_, err = tx.ExecContext(ctx, query, blob.BlobHash, blob.CreatedTS.Unix())
+	} else {
+		_, err = r.db.conn.ExecContext(ctx, query, blob.BlobHash, blob.CreatedTS.Unix())
+	}
+
+	if err != nil {
+		return fmt.Errorf("inserting blob: %w", err)
+	}
+
+	return nil
+}
+
+func (r *BlobRepository) GetByHash(ctx context.Context, hash string) (*Blob, error) {
+	query := `
+		SELECT blob_hash, created_ts
+		FROM blobs
+		WHERE blob_hash = ?
+	`
+
+	var blob Blob
+	var createdTSUnix int64
+
+	err := r.db.conn.QueryRowContext(ctx, query, hash).Scan(
+		&blob.BlobHash,
+		&createdTSUnix,
+	)
+
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("querying blob: %w", err)
+	}
+
+	blob.CreatedTS = time.Unix(createdTSUnix, 0)
+	return &blob, nil
+}
+
+func (r *BlobRepository) List(ctx context.Context, limit, offset int) ([]*Blob, error) {
+	query := `
+		SELECT blob_hash, created_ts
+		FROM blobs
+		ORDER BY blob_hash
+		LIMIT ? OFFSET ?
+	`
+
+	rows, err := r.db.conn.QueryContext(ctx, query, limit, offset)
+	if err != nil {
+		return nil, fmt.Errorf("querying blobs: %w", err)
+	}
+	defer CloseRows(rows)
+
+	var blobs []*Blob
+	for rows.Next() {
+		var blob Blob
+		var createdTSUnix int64
+
+		err := rows.Scan(
+			&blob.BlobHash,
+			&createdTSUnix,
+		)
+		if err != nil {
+			return nil, fmt.Errorf("scanning blob: %w", err)
+		}
+
+		blob.CreatedTS = time.Unix(createdTSUnix, 0)
+		blobs = append(blobs, &blob)
+	}
+
+	return blobs, rows.Err()
+}