feat: add i18n descriptions to all hands and channels (#22)

Add [i18n.zh], [i18n.zh-TW], [i18n.ja], [i18n.ko], [i18n.de], [i18n.es]
sections with translated descriptions to:
- 15 Hand TOML files (hands/*/HAND.toml)
- 44 Channel TOML files (channels/*.toml)

This enables the website to display localized Hand and Channel descriptions
based on the user's selected language.

channels/mattermost.toml

@@ -5,6 +5,24 @@ category = "enterprise"
 icon = "🔵"
 protocol = "websocket"
 
+[i18n.zh]
+description = "Mattermost 适配器，在 Mattermost 工作区中发送团队消息和通知"
+
+[i18n.zh-TW]
+description = "Mattermost 適配器，在 Mattermost 工作區中發送團隊訊息和通知"
+
+[i18n.ja]
+description = "Mattermostアダプター、Mattermostワークスペースでのチームメッセージングと通知"
+
+[i18n.ko]
+description = "Mattermost 어댑터, Mattermost 워크스페이스에서 팀 메시지 및 알림 전송"
+
+[i18n.de]
+description = "Mattermost-Adapter für Team-Messaging und Benachrichtigungen in Mattermost-Workspaces"
+
+[i18n.es]
+description = "Adaptador de Mattermost para mensajería de equipo y notificaciones en espacios de trabajo Mattermost"
+
 [metadata]
 url = "https://mattermost.com"
 docs = "https://api.mattermost.com"