Docs sweep: replace ray_run.py / launch_on_ray / ray_tpu references after deletion (#5028, #5031)

[yonromai]

🤖 Follow-up to the Ray deletion PRs (#5028, #5031). Non-code files still reference modules that have been deleted. A mechanical sed pass would produce misleading docs because scripts/iris/dev_tpu.py is not a drop-in replacement for ray_run.py — it's a persistent-session tool (allocate → execute → release), not a one-shot submitter. Flags diverge: --no_wait, --extra, --cluster, --entrypoint-num-*, --auto-stop, --submission-id have no equivalent; --env_vars KEY VALUE becomes -e KEY=VALUE only on subcommands. The Levanter launch_on_ray references are similarly workflow-specific.

Files to update (owners in parens)

From #5028 (ray_run.py / marin.cluster.ray references)

Tutorials (docs team)

• docs/explanations/executor.md:108
• docs/tutorials/train-dpo.md:143
• docs/tutorials/train-an-lm.md:152
• docs/tutorials/tpu-cluster-setup.md:101-109 (may be deleted wholesale with the operator-tooling cleanup)

Recipes

• docs/recipes/add_scaling_heuristic.md:45,179 (uses --cluster marin-us-central2 — needs owner input on target cluster)

Skills / planning

• .agents/skills/ferries/SKILL.md:127,141
• .agents/skills/architecture/SKILL.md:16,27
• .agents/projects/ferry_framework.md:277

Runbooks / experiment READMEs

• experiments/tootsie/BABYSITTING.md:15,62,69,76,84 (tootsie operators)
• experiments/grug/README.md:43
• experiments/README_sft.md:12,44,47

Docstring / header Usage: lines

• experiments/tutorials/exp1077_reproduce_dclm_1b1x.py:14
• experiments/tutorials/exp1078_reproduce_dclm_7b1x.py:14
• experiments/rollout_data/{synthetic1,swe_rebench_openhands,principia,nemotron_terminal,gpt_oss_rollouts,superior_reasoning,coderforge}.py (7 files, all Usage: at ~line 7)
• experiments/ferries/daily.py:14 (prose reference)

From #5031 (launch_on_ray / ray_tpu references)

Levanter docs

• lib/levanter/docs/Getting-Started-TPU-VM.md — 5 references to launch_on_ray (feature description, caveats, usage example, deprecation note)

Questions to resolve before sweeping

1. Canonical one-shot launcher for executor-driven experiments in the Iris era — is it just python experiments/foo.py, assuming executor_main routes via fray → Iris?
2. --no_wait equivalent for detached/long-running launches (ferries, tootsie).
3. docs/tutorials/tpu-cluster-setup.md — rewrite or delete with the operator-tooling cleanup (scripts/ray/*, 18 × infra/marin-*.yaml)?
4. lib/levanter/docs/Getting-Started-TPU-VM.md — rewrite the launch_on_ray sections to point at the fray/Iris TPU path, or delete them entirely if that workflow is deprecated?

[yonromai]

🤖 Stage-4 doc sweep is up in #5076. Two residuals intentionally deferred to later stages — logging here so they don't get lost:

1. docs/dev-guide/tpu_observability.md — references ray-user-node-type / ray-marin-* VM labels in gcloud queries. Still accurate for live Ray cluster nodes; needs a pass (rewrite or delete) once Ray VMs are torn down.
2. lib/zephyr/README.md, lib/zephyr/AGENTS.md, lib/fray/AGENTS.md — list Ray as a current backend. Correct until the fray v2 Ray backend is dropped; sweep these at that point.