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/slack.toml

@@ -5,6 +5,24 @@ category = "enterprise"
 icon = "💜"
 protocol = "websocket"
 
+[i18n.zh]
+description = "Slack 机器人适配器，在 Slack 工作区中收发消息"
+
+[i18n.zh-TW]
+description = "Slack 機器人適配器，在 Slack 工作區中收發訊息"
+
+[i18n.ja]
+description = "Slackボットアダプター、Slackワークスペースでのメッセージ送受信"
+
+[i18n.ko]
+description = "Slack 봇 어댑터, Slack 워크스페이스에서 메시지 송수신"
+
+[i18n.de]
+description = "Slack-Bot-Adapter zum Senden und Empfangen von Nachrichten in Slack-Workspaces"
+
+[i18n.es]
+description = "Adaptador de bot Slack para enviar y recibir mensajes en espacios de trabajo Slack"
+
 [metadata]
 url = "https://slack.com"
 docs = "https://api.slack.com/docs"