Split the diffs viewer Shiki language pack into an external publishable plugin.
The diffs plugin keeps the default curated syntax set, while the new @openclaw/diffs-language-pack package carries the extended Shiki languages for npm and ClawHub distribution. The install metadata includes the external ClawHub spec, and the curated C# alias set keeps both c# and cs supported without the language pack.
Co-authored-by: Dallin Romney <dallinromney@gmail.com>
