Bold/italic closed by CJK punctuation renders as literal asterisks in markdown

Description

In the desktop and web markdown renderer, emphasis whose closing marker sits directly against CJK punctuation renders as literal asterisks instead of bold/italic. For example 含**「重点」**内容 shows the ** as plain text and 「重点」 stays unstyled. Emphasis at normal (ASCII / whitespace) boundaries works fine, so it only bites on CJK text — very visible in zh/ja/ko conversations.

Steps to reproduce

1. Send or display a line containing bold/italic text closed by CJK punctuation, e.g. 含**「重点」**内容.
2. Look at the rendered markdown in the TUI / web / desktop UI.

Expected: 「重点」 is bold and the asterisks are consumed. Actual: the ** markers show up verbatim and 「重点」 is not emphasized.

Screenshot and/or share link

Renderer tokenization issue; no UI screenshot. Before/after is covered by the unit tests in the linked PR.

Operating System

macOS (also reproducible in the web UI, OS-independent)

Terminal

N/A — affects the rendered markdown view, not a specific terminal