Port AOT-safe SetForegroundSessionRequest from reference impl (c63feb2)

[Copilot]

Ports reference implementation commit c63feb2: replaces the ad-hoc Map.of("sessionId", sessionId) parameter bag in setForegroundSessionId() with a dedicated named request type, matching the .NET SDK's shift from an anonymous object to an explicit record for serialization clarity.

Changes

• json/SetForegroundSessionRequest.java (new) — named record with @JsonProperty("sessionId"), parallel to the existing SetForegroundSessionResponse
• CopilotClient.java — setForegroundSessionId() now constructs new SetForegroundSessionRequest(sessionId) instead of Map.of(...)
• .lastmerge — updated to c63feb2794786342d57936c13d28c250e723c676

// Before
.invoke("session.setForeground", Map.of("sessionId", sessionId), SetForegroundSessionResponse.class)

// After
.invoke("session.setForeground", new SetForegroundSessionRequest(sessionId), SetForegroundSessionResponse.class)

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• mvn spotless:apply has been run to format the code
• mvn clean verify passes locally

Does this introduce a breaking change?

• Yes
• No

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