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/module.go

@@ -0,0 +1,40 @@
+package database
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"git.eeqj.de/sneak/vaultik/internal/config"
+	"go.uber.org/fx"
+)
+
+// Module provides database dependencies
+var Module = fx.Module("database",
+	fx.Provide(
+		provideDatabase,
+		NewRepositories,
+	),
+)
+
+func provideDatabase(lc fx.Lifecycle, cfg *config.Config) (*DB, error) {
+	// Ensure the index directory exists
+	indexDir := filepath.Dir(cfg.IndexPath)
+	if err := os.MkdirAll(indexDir, 0700); err != nil {
+		return nil, fmt.Errorf("creating index directory: %w", err)
+	}
+
+	db, err := New(context.Background(), cfg.IndexPath)
+	if err != nil {
+		return nil, fmt.Errorf("opening database: %w", err)
+	}
+
+	lc.Append(fx.Hook{
+		OnStop: func(ctx context.Context) error {
+			return db.Close()
+		},
+	})
+
+	return db, nil
+}