fix: subscribing to events should not be blocked by agent actor state

[mattjohnsonpint]

Checking agent status when subscribing to an event stream should not be blocked by the agent actor's state. We can just go directly to the database.

Additionally, in cases where we do want to talk to the actor, there are a couple more error states to consider.

[Copilot]

Pull Request Overview

This PR ensures event subscription does not depend on the actor’s availability by fetching agent status directly from the database, and adds new error conditions when querying the actor.

• Switch SubscribeForAgentEvents to use direct DB lookup for status
• Extend GetAgentInfo to handle ErrDead and ErrRemoteSendFailure
• Bump runtime version and adjust dates in CHANGELOG

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
runtime/actors/subscriber.go	Replaced actor call with direct DB lookup for agent status
runtime/actors/agents.go	Added new actor error cases (ErrDead, ErrRemoteSendFailure)
CHANGELOG.md	Updated to v0.18.1 and fixed release dates for SDK entries

Comments suppressed due to low confidence (1)

runtime/actors/subscriber.go:38

• Add unit tests for SubscribeForAgentEvents to cover the new direct DB fallback path, ensuring subscriptions succeed when the actor is unresponsive.

	if a, err := getAgentInfoFromDatabase(ctx, agentId); err != nil {