docs: align docs with actual auth/authType behaviour

[IzaakGough]

Summary

• Correct the v1 EventContext TSDoc so it documents auth and authType as Realtime Database-specific behavior.
• Clarify that callable auth uses https.CallableContext.auth, and that non-RTDB events leave authType unset rather than null.

Problem/Root Cause

The existing EventContext comments described auth as applying to both Realtime Database triggers and callable functions, and described authType as null for non-RTDB events. That does not match the actual v1 runtime behavior: the SDK only populates EventContext.auth and EventContext.authType for Realtime Database triggers, while callable functions expose auth on https.CallableContext instead. For non-RTDB EventContext events, authType is not set.

Solution/Changes

Update the EventContext TSDoc to describe the real behavior implemented by the v1 SDK:

• mark EventContext.auth as Realtime Database-only
• document unauthenticated Realtime Database events as auth: null
• document callable auth on https.CallableContext.auth instead of EventContext.auth
• describe authType as Realtime Database-only and not set for non-RTDB events

Testing

• Manually verified with the Emulator Suite:
• Realtime Database v1 trigger logged authType: "ADMIN" with auth: undefined for an admin write.
• Firestore v1 trigger logged auth: undefined and authType: undefined.

[gemini-code-assist]

Code Review

This pull request updates the JSDoc documentation for the auth and authType properties of the EventContext interface in src/v1/cloud-functions.ts. It clarifies that these fields are only populated for Realtime Database triggers, explains their behavior for unauthenticated users, and directs users to https.CallableContext.auth for Callable functions. I have no feedback to provide.