* fix(workbench): render LaTeX in assistant messages
* fix(workbench): harden streamed math rendering
* fix(workbench): preserve streamed math boundaries
* refactor(workbench): use standard math syntax
* fix(workbench): preserve math in course link labels
* fix(workbench): disambiguate single-dollar math
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Co-authored-by: wyuc <wang-yc24@mails.tsinghua.edu.cn>