Add namespaces support (CRUD, RBAC, namespace-scoped users)

Context

The Weaviate server adds a Namespaces feature in 1.38.0+ (see weaviate-python-client PR #2033). This adds full CRUD support, a new `manage_namespaces` RBAC permission, and namespace-scoped DB users. The CLI should expose these capabilities so users can administer namespaces, grant namespace permissions, and bind users to namespaces from the command line.

Scope

• Add `create namespace`, `get namespace`, `delete namespace` subcommands (with `--all` for listing).
• Add a `NamespaceManager` with create/get/list/delete operations and JSON output.
• Extend `parse_permission` to recognize `manage_namespaces:`, and document it in `PERMISSION_HELP_STRING`.
• Render `namespaces_permissions` in role output (text + JSON).
• Add `--namespace` option to `create user` and surface the user's namespace in `get user` output.
• Add unit tests for the manager, permission parsing, and namespace-aware user creation.
• Update operating and contributing skills to document the new commands and patterns.

Files Involved

• `weaviate_cli/defaults.py`
• `weaviate_cli/commands/create.py`, `get.py`, `delete.py`
• `weaviate_cli/managers/namespace_manager.py` (new)
• `weaviate_cli/managers/user_manager.py`, `role_manager.py`
• `weaviate_cli/utils.py`
• `test/unittests/test_managers/test_namespace_manager.py` (new) and others
• `.claude/skills/operating-weaviate-cli/`
• `.claude/skills/contributing-to-weaviate-cli/`

Acceptance Criteria

• `weaviate-cli create namespace --name ` creates a namespace and supports `--json`.
• `weaviate-cli get namespace [--name ] [--all]` retrieves one or all namespaces.
• `weaviate-cli delete namespace --name ` deletes a namespace.
• `--permission manage_namespaces:` parses correctly and produces a valid RBAC permission.
• `weaviate-cli create user --user_name foo --namespace bar` creates a namespace-scoped user.
• `weaviate-cli get user --user_name foo` shows the namespace.
• `weaviate-cli get role` text/JSON output includes `namespaces_permissions`.
• Unit tests pass for new functionality.
• `make lint` and `make test` pass.
• Skill docs (operating + contributing) updated.

Constraints

• Requires Weaviate 1.38.0+; rely on the python client's version check rather than re-implementing in the CLI.
• Follow the existing defaults dataclass + command-to-manager pattern.

🤖 Generated with Claude Code

Start with the defaults dataclass and command-to-manager pattern in weaviate_cli/defaults.py and the commands in create.py, get.py, and delete.py. Read the new namespace_manager.py alongside user_manager.py, role_manager.py, and utils.py, then inspect the named unit tests. Done means the namespace commands, permissions, user and role output, skill docs, make lint, and make test satisfy the acceptance criteria.