docs(apify-actor-development): clarify apify push needs apify login, not just APIFY_TOKEN

[DaveHanns]

Rationale

The ## Prerequisites and setup (mandatory) section currently tells agents that in headless / CI environments the CLI "automatically reads APIFY_TOKEN from the environment... no explicit login needed." That is accurate for apify info and apify api, but empirically not true for apify push, which reads its token from ~/.apify/auth.json (populated by apify login) and does not consult APIFY_TOKEN at deploy time.

The visible failure mode is confusing: an agent following the current guidance sees apify info succeed, concludes it is authenticated, then apify push fails with a 401 wrapped in unstructured error prose (exit 1). This PR amends the last paragraph of that section with a headless / CI caveat so agents run apify login --token "$APIFY_TOKEN" at session start.

While in the same paragraph, this also documents that apify push has no --yes / --no-prompt flag — --force is the one to use for overwriting an existing build.

Added content (preview)

Headless / CI note: apify info and apify api read APIFY_TOKEN from the environment, but apify push reads its token from ~/.apify/auth.json populated by apify login. In a non-interactive environment where you cannot complete the OAuth flow, run apify login --token "$APIFY_TOKEN" once at session start; otherwise apify push fails with a 401 despite apify info succeeding.

apify push is already non-interactive once a token is stored — there is no --yes / --no-prompt flag. Use apify push --force to skip the confirmation when overwriting a build of an existing version.

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