When a user leaves or unpins a chat channel, the related chat window now closes automatically. This keeps the messaging workspace cleaner and avoids confusion from inactive chat windows remaining open.

Before this commit, leaving or unpin a channel kept the chat window open.
This commit forces the closing of the chat window when either action is made.

task-4452932

Users will now only see the real-time connection lost alert if the disconnection lasts more than 15 seconds. This reduces unnecessary alerts for brief or unstable network interruptions, making the experience less disruptive.

Before this PR, the "real-time connection lost" alert was displayed right after the disconnection was detected.
This PR adds a 15s delay to avoid spamming the alert on unstable connexion.

Task-4453176

The update removes an unnecessary notification when a chat conversation is unpinned. This makes the messaging and live chat experience less distracting while keeping conversation management unchanged.

task-4452840

Related to odoo/enterprise#76559

Live chat sessions are now ordered by when they were created, with the newest sessions appearing first in the kanban view. This helps teams see recent conversations more quickly and prioritize current customer interactions.

This commit changes the order of livechat sessions in the kanban view to sort them descending by their `create_date`.

task-4452928

WhatsApp conversations no longer show a notification when a conversation is unpinned. This reduces unnecessary messages in the interface and keeps the user experience cleaner.

task-4452840

Related to odoo/odoo#192540