Add Chat service for im.chat.* support (#423)

[mesilov]

Q	A
Bug fix?	no
New feature?	yes
Deprecations?	no
Issues	Fix #423
License	MIT

Summary

Adds a new Chat service under the IM scope that wraps eight Bitrix24 REST methods for chat management:

• im.chat.add — create a chat
• im.chat.get — resolve a chat by linked entity type and id
• im.chat.leave — remove the current user from a chat
• im.chat.mute / im.chat.muteByDialog — mute notifications by CHAT_ID or DIALOG_ID (two explicit methods to keep each endpoint shape typed)
• im.chat.setOwner — transfer chat ownership
• im.chat.updateAvatar — update chat avatar (base64)
• im.chat.updateColor — update chat color
• im.chat.updateTitle — update chat title

Chat-specific string parameters are modelled as scope-local PHP 8.1 string-backed enums: ChatType, ChatColor, ChatEntityType. Result types: ChatItemResult + ChatResult (returns ?ChatItemResult to reflect that im.chat.get returns null when no chat matches).

IMServiceBuilder::chat() accessor wires the new service into the existing IM scope factory.

Usage

use Bitrix24\SDK\Services\IM\Chat\ChatEntityType;
use Bitrix24\SDK\Services\IM\Chat\ChatType;

$chatService = $serviceBuilder->getIMScope()->chat();

$chatId = $chatService->add(
    users: [42, 43],
    chatType: ChatType::Closed,
    title: 'Project discussion',
    chatEntityType: ChatEntityType::Calendar,
    entityId: 'PROJECT_42',
)->getId();

$chat = $chatService->get(ChatEntityType::Calendar, 'PROJECT_42')->chat();
if ($chat !== null) {
    $chatService->updateTitle($chat->ID, 'Renamed chat');
}

Test plan

• make lint-cs-fixer
• make lint-rector
• make lint-phpstan
• make lint-deptrac
• make test-unit — 768 tests, 1959 assertions
• make test-integration-im-chat — 12 tests, 17 assertions, all green against real portal

Closes #423

[mesilov]

@copilot resolve the merge conflicts in this pull request