Add IM Chat entity and manager methods

[mesilov]

Problem

The live Bitrix24 im scope exposes two chat methods that are not currently implemented in the SDK service layer:

• im.chat.getEntityChat
• im.chat.setManager

These methods were found while auditing the remaining unsupported im methods after the im.department.* work. They are also listed in the umbrella IM scope tracking issue #422.

Documentation

• im.chat.getEntityChat — no official public apidocs.bitrix24.com method page was found via the Bitrix24 documentation MCP or direct apidocs search.
• im.chat.setManager — no official public apidocs.bitrix24.com method page was found via the Bitrix24 documentation MCP or direct apidocs search.
• Scope overview: https://apidocs.bitrix24.com/api-reference/chats/index.html

Proposed solution

Add SDK support in the existing IM Chat service area, following the current Bitrix24\SDK\Services\IM\Chat\Service\Chat conventions:

• Add typed service methods for im.chat.getEntityChat and im.chat.setManager.
• Add result wrappers where the raw response shape requires them.
• Use ApiEndpointMetadata entries with the exact REST method names and documentation links when an official method page becomes available.
• Add focused unit tests for request payload mapping and result types.
• Add integration coverage against the live Bitrix24 playground when the methods can be called safely.

Acceptance criteria

• Factory::getServiceBuilder()->getIMScope()->chat() exposes SDK methods for im.chat.getEntityChat and im.chat.setManager.
• The implementation uses the exact live REST method names and keeps the im scope metadata.
• Unit tests cover payload mapping for both methods.
• Integration tests cover the live response shape or document any live-environment blocker in the task plan.
• make sdk-coverage-v1-show no longer lists im.chat.getentitychat or im.chat.setmanager as unsupported in the im scope.