Require pushed environments for eval uploads

[d42me]

Summary

• Block prime eval push from creating uploads against bare local environment names.
• Prompt users to run prime env push <env> and retry with an owner-qualified environment slug before uploading.
• Update eval push help/tests to reflect that uploads require a published environment.

Validation

• uv run pytest packages/prime/tests/test_eval_push.py -q
• uv run pytest packages/prime/tests/test_eval_help.py packages/prime/tests/test_eval_push.py -q
• uv run ruff check packages/prime/src/prime_cli/commands/evals.py packages/prime/tests/test_eval_push.py
• uv run ty check packages/prime/src/prime_cli/commands/evals.py packages/prime/tests/test_eval_push.py

---

Note

Medium Risk
Changes prime eval push behavior to hard-fail when given an unqualified environment name, which may break existing workflows/scripts that relied on local env names.

Overview
prime eval push now requires a published environment slug (owner/name) when associating an environment with an uploaded evaluation; passing a bare env name triggers a clear error prompting prime env push and a retry with an owner-qualified slug.

CLI help text, examples, and error tips were updated accordingly, and tests were adjusted/added to assert the new enforcement and that the API receives environments=[{"slug": ...}].

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