Clarify whether 'agentv eval <file>' is a supported alias for 'agentv eval run'

[christso]

Summary

On agentv@4.27.0, agentv eval <file> ... still works as an alias for agentv eval run <file> ..., but agentv eval --help only documents subcommands (run, assert, aggregate).

That mismatch is easy to misread as “run is mandatory”, which caused review confusion downstream when evaluating whether docs/examples should use:

• agentv eval <file> ...
• agentv eval run <file> ...

Repro

agentv --version
# 4.27.0

agentv eval --help

Current help shows:

agentv eval <subcommand>
> Evaluation commands

where <subcommand> can be one of:
- run
- assert
- aggregate

But this still executes the eval path directly:

agentv eval ./evals/some.eval.yaml --target llm

Expected

One of these should be made true and explicit:

1. If agentv eval <file> ... is supported intentionally

   • document it in help as a supported shorthand / alias for run
   • ideally show both forms or mention that bare eval dispatches to run

2. If run is meant to be the only supported form

   • reject agentv eval <file> ... with a clear error
   • update any compatibility behavior accordingly

Why this matters

Right now the CLI behavior and the help text disagree. Humans reviewing docs or automation tend to trust --help, so they conclude that run is required even though the binary still accepts the no-subcommand form.

That ambiguity leaks into downstream docs, workflows, and PR reviews.