Add 'dremio space' commands and reject single-component paths in 'folder create'

[sandhyasun]

Summary

The CLI currently blurs the distinction between spaces and folders. When dremio folder create "foo" is called with a single-component path, it silently rewrites it to CREATE SPACE "foo" SQL. This doesn't match the backend behavior and hides an important semantic difference.

Current behavior

In drs/commands/folder.py (lines 54-62):

async def create_folder(client: DremioClient, path: str) -> dict:
    parts = parse_path(path)
    if len(parts) == 1:
        sql = f'CREATE SPACE "{parts[0]}"'    # silently converts to CREATE SPACE
    else:
        quoted = quote_path_sql(path)
        sql = f"CREATE FOLDER {quoted}"
    return await run_query(client, sql)

Problems

1. Semantic mismatch: The backend treats spaces and folders as distinct entities. CREATE FOLDER with a single-component path is explicitly rejected by CatalogImpl.validateFolder() with: "Folder path should be fully qualified. Path must include a space or source." The CLI should respect this distinction rather than silently converting.

2. Pre-Space Plugin incompatibility: On projects without Space Plugin enabled, CREATE SPACE SQL doesn't exist, so dremio folder create "foo" would fail with an unhelpful error about unsupported SQL syntax.

3. Missing concept: There is no dremio space command group at all. Spaces are a first-class catalog concept and deserve their own CLI surface.

Proposed changes

1. Add dremio space command group with at least:

   • dremio space list — list all spaces (filter folder list to containerType: SPACE)
   • dremio space create <name> — runs CREATE SPACE "<name>"
   • dremio space delete <name> — deletes a space
   • dremio space get <name> — get space metadata and children

2. Reject single-component paths in dremio folder create — return an error like: "Cannot create a top-level folder. Use dremio space create <name> to create a space, or provide a fully qualified path like <space>.<folder>."

3. Keep dremio folder list as-is (shows both spaces and sources), or optionally add a --type filter.

Backend reference

• CreateSpaceHandler.java — handles CREATE SPACE SQL
• CreateFolderHandler.java — handles CREATE FOLDER SQL
• CatalogImpl.validateFolder() — rejects single-component folder paths
• CatalogOptions.SQL_SPACE_QUERIES_ENABLED — gates CREATE SPACE support (default: true)