feat(actors): add apify actors exists, ls --name-only, and improve push name-collision UX

[DaveHanns]

Summary

Adds two small, scripting-friendly primitives for asking "is this Actor name available?" and improves the CLI transcript when apify push reuses an existing Actor or fails on a name conflict.

• New: apify actors exists <name> — exits 0 if the Actor exists, 1 if not. Accepts a short name (resolved in the logged-in user's namespace), a fully qualified <username>/<name>, or an Actor ID. --json emits { exists, query, resolvedId, actor }.
• New flag: apify actors ls --name-only — prints one <username>/<name> per line and short-circuits before the per-row hydration Promise.all (which normally fetches an extra .get() + runs list per row for the table). Composes with --my, --limit, --offset, --desc.
• apify push transcript when the Actor already exists in your namespace: previously silent — now emits Info: Updating existing Actor <username>/<name> (id=…).
• apify push error when POST /v2/acts fails on a duplicate/reserved name: the raw API message (e.g. Actor name is already used) is rewritten with actionable next steps.

Motivation

apify actors ls --my and apify push are the entry points people reach for when scripting Actor management (CI pipelines, template scaffolders, agent-driven tooling). Two workflows are awkward today:

1. "Is this name free?" has no first-class answer

apify actors ls --my prints a decorated table (Runs / Last run / Build columns) that is hard to grep and, per row, does an extra apifyClient.actor(id).get() + runs list fetch just for the display. Callers scripting a collision check end up reaching for the raw REST API instead — e.g.

curl -sH "Authorization: Bearer $APIFY_TOKEN" \
  'https://api.apify.com/v2/acts?my=1&limit=100' \
  | jq -r '.data.items[].name'

With this PR:

apify actors ls --my --name-only
# apify-user/my-crawler
# apify-user/hello-world

apify actors exists my-crawler && echo taken || echo free

And the canonical scripted "create only if free" pattern becomes:

apify actors exists my-crawler || apify push

2. apify push is silent when it reuses an existing Actor

The relevant branch in src/commands/actors/push.ts today (before this PR) is:

actor = (await apifyClient.actor(`${usernameOrId}/${actorConfig!.name}`).get())!;
if (actor) {
    actorId = actor.id;
    // <-- no log emitted; identical-looking to the "create" branch below
} else {
    ...
    actor = await apifyClient.actors().create(newActor);
    info({ message: `Created Actor with name ${actorConfig!.name} on Apify.` });
}

If a user (or an automated pipeline) forgets they have already used a given name in their namespace, the push silently overwrites the previously deployed Actor with no visible signal. After this PR the transcript shows explicitly:

Info: Updating existing Actor apify-user/my-crawler (id=E2jjCZBezvAZnX8Rb).
Info: Deploying Actor 'my-crawler' to Apify.

3. POST /v2/acts duplicate-name errors are opaque

The pre-flight apify.actor("<user>/<name>").get() doesn't catch (a) reserved / conflicting names, or (b) a race where a parallel process claimed the name between the .get() and the .create(). When that happens the surfaced error is the raw API message with no next step:

Error: Actor name is already used

After this PR:

Error: Cannot create Actor "my-crawler": the name is unavailable on the Apify platform (Actor name is already used).
Next steps:
  - Rename the Actor: edit the "name" field in .actor/actor.json and run 'apify push' again.
  - Push to an existing Actor: 'apify push <actor-id-or-username/name>'.
  - List names you already own: 'apify actors ls --my --name-only'.
  - Check whether a name is free: 'apify actors exists <name>'.

Design notes

• Exit-code convention for exists: 0 = exists (name is taken), 1 = not found. Chosen so a bare apify actors exists foo && echo taken idiom works without extra flags, matching test, grep, gh repo view, kubectl get.
• Short-name resolution in exists: if the argument has no / and doesn't look like an Actor ID (/^[A-Za-z0-9]{17}$/), it's resolved as <logged-in-user>/<name>, so apify actors exists my-crawler targets the user's own namespace by default.
• --name-only short-circuits before hydration: the existing ls code path awaits a per-row apifyClient.actor(id).get() + runs list for the table. When the caller only needs identifiers, that work is wasted (and can be slow for --limit 100), so --name-only returns straight from apifyClient.actors().list().
• Error rewrite in push is defensive: the name-conflict detection matches on already used, not available, or duplicate in the error message. If the pattern doesn't match, the original error is re-thrown unchanged.

Test plan

• apify actors ls --my --name-only prints <username>/<name> lines and exits 0.
• apify actors ls --my --name-only with zero Actors prints nothing and exits 0.
• apify actors ls --my --name-only --json still returns the JSON payload (the flag is a no-op under --json).
• apify actors exists <name-you-own> → exit 0, prints Actor "<user>/<name>" exists (id=…)..
• apify actors exists <name-that-does-not-exist> → exit 1, prints Actor "<user>/<name>" does not exist..
• apify actors exists <name> --json → exit 0/1 and JSON with exists: true/false.
• apify actors exists apify/hello-world resolves the fully-qualified name (doesn't prepend the logged-in username).
• apify push in a directory whose .actor/actor.json names an Actor the user already owns prints Info: Updating existing Actor ….
• apify push where POST /v2/acts fails with a duplicate-name response prints the rewritten error with the four suggested next steps.
• pnpm tsc --noEmit passes.

Files changed

• src/commands/actors/exists.ts — new command.
• src/commands/actors/ls.ts — add --name-only flag; short-circuit before hydration.
• src/commands/actors/push.ts — emit Info: Updating existing Actor …; rewrite name-conflict errors with actionable next steps.
• src/commands/actors/_index.ts — register ActorsExistsCommand.

Surfaced during an evaluation of Apify surfaces for agent-driven Actor development.