fix(composer): support Chinese slash command trigger

[Usernames686]

Problem

When using a Chinese IME, the key that normally produces / produces 、, so users must switch input methods before opening slash commands.

Fixes #597.

Fix

Treat 、 as an input-level alias for / when triggering slash commands. The alias is normalized to the existing internal / trigger, and command selection still creates the canonical slash-command reference.

The normalization is limited to slash-command triggering and token replacement. It does not replace normal Chinese punctuation in message content.

Tests

• / still triggers slash commands
• 、 triggers the same slash command flow
• normal Chinese 、 remains unchanged
• selected commands are serialized with /
• composing Enter does not select a slash command