Add a `whoami` tool to the Apify MCP server

[vystrcild]

Summary

Add a lightweight whoami tool that returns the identity of the account the current API token is authenticated as.

Motivation

Sentry's MCP server has a handy whoami tool that tells you which account the connection is authenticated as. A whoami on the Apify MCP server would let an agent confirm which Apify account/identity it's operating as — useful for debugging, multi-account setups, and giving the model awareness of whose data and usage it's touching.

Proposed behavior

• Wraps the Get user endpoint: GET /v2/users/me (https://docs.apify.com/api/v2/users-me-get).
• Returns the authenticated user's identity: username, user ID, email.
• Note: plan, email, and profile are omitted when the token belongs to an Actor run, so behavior differs depending on auth context.

Open questions

• Which fields to expose vs. redact (plan tier, usage/limits, billing info)?
• Naming: whoami (matches Sentry convention) vs. something more explicit like get-current-user?

Reference

Suggested by Jan in #product-ai.