Add custom types, version command, and restore --verify flag

- Add internal/types package with type-safe wrappers for IDs, hashes,
  paths, and credentials (FileID, BlobID, ChunkHash, etc.)
- Implement driver.Valuer and sql.Scanner for UUID-based types
- Add `vaultik version` command showing version, commit, go version
- Add `--verify` flag to restore command that checksums all restored
  files against expected chunk hashes with progress bar
- Remove fetch.go (dead code, functionality in restore)
- Clean up TODO.md, remove completed items
- Update all database and snapshot code to use new custom types

internal/database/repositories.go

@@ -75,6 +75,11 @@ func (r *Repositories) WithTx(ctx context.Context, fn TxFunc) error {
 	return tx.Commit()
 }
 
+// DB returns the underlying database for direct queries
+func (r *Repositories) DB() *DB {
+	return r.db
+}
+
 // WithReadTx executes a function within a read-only transaction.
 // Read transactions can run concurrently with other read transactions
 // but will be blocked by write transactions. The transaction is