Drop deprecated model / dataset / training commands

The `list-models`, `summarize-model`, `deploy-model`, and `dataset`
commands targeted services that are no longer part of the product
surface. Cutting them entirely (CLI + API client + tests) rather than
leaving shells that hit dead endpoints.

Deleted (16 files):

- remyxai/api/{datasets,deployment,evaluations,models,tasks,user}.py
  — API clients for retired services. `tasks.py` covered the legacy
  myxmatch / benchmark / classifier / detector / generator /
  datacomposer surface; all gone.
- remyxai/cli/{dataset,deployment,evaluation}_actions.py
  — per-command action handlers
- tests/cli/test_{deployment,evaluation}_actions.py
- tests/api/test_{dataset,deployment,models,tasks,user}.py

Tightened (4 files):

- remyxai/cli/commands.py — removed 3 imports + 4 command
  registrations; module docstring refreshed
- tests/api/test_lazy_api_key.py — removed test methods that
  referenced the deleted API client modules
- tests/cli/test_commands.py — replaced the per-command wiring
  tests for the removed commands with a `cli --help` regression that
  asserts the current command groups are exposed and the deprecated
  ones aren't listed
- README.md — dropped the four deprecated rows from the
  command-reference table

Verification

- `remyxai --help` shows only `interests`, `outrider`, `papers`,
  `search`
- Full test suite: 121 passed, 15 skipped (live integration tests,
  expected)

Author: smellslikeml

README.md

@@ -71,10 +71,6 @@ Run any command with `--help` for full flag listings and examples.
 | `remyxai outrider init` | Install Outrider on a GitHub repo via the Remyx App |
 | `remyxai search list` | List recently added research assets (papers + Docker images) |
 | `remyxai search info <arxiv-id>` | Asset details |
-| `remyxai list-models` | List available trained models on your account |
-| `remyxai summarize-model <name>` | Show a model's summary |
-| `remyxai deploy-model <name> <up\|down>` | Bring a containerized deployment up or down |
-| `remyxai dataset <action> [name]` | Manage datasets (`list`, `download`, `delete`) |
 
 ## Outrider install — what happens