#430 Port the GitHub and GitHub Split themes

[Anonymous]

Originally created by: kristofferR

Goal

Port GitHub and GitHub Split into the catalog (#426), on Chatpane's hooks (#424).

Source (MIT)

darkpiv's fork https://github.com/darkpiv/fmess at 1774715: src-tauri/themes/github.css, github-split.css (sources in themes-src/github/, Octicons MIT, Primer primitives MIT). Author: darkpiv. Its notes say it was never seen running, so expect real selector work.

Port

• Rename fMess hooks to Chatpane's; drop the header strip and the unread count drawn in it (--fmess-title-bar is always 0 in Chatpane).
• The "check running" typing dot pulses forever: make it static.
• Header: /* Chatpane theme, name, author: darkpiv, preview colours.

Testing

Light and dark: the diff-line messages (yours as additions, theirs as deletions), hunk-header dates, reactions, replying, the composer, menus. Split variant at narrow and wide windows.

Part of [#434].