Six more palettes, taking the picker to twelve

Catppuccin, Solarized, Ayu, Kanagawa, Everforest and Primer, each with the
light and dark variant its own project publishes: Latte and Mocha, Lotus
and Wave, and so on. Values were fetched from each project's own repository
and recorded in .palette-sources/palettes-upstream.md, with the two tiers
no project publishes marked derived rather than passed off as upstream.

Four candidates were rejected rather than adapted. Nord and Synthwave '84
publish no light variant, and inventing one is not porting a theme.
Monokai is proprietary and its licence forbids redistribution. Material
Theme has become a commercial product whose repository no longer publishes
a palette at all.

Body text is now lifted for contrast like every other text tone rather
than exempted and merely checked. Most of these palettes target their own
~4.5:1 for body text where ihasmail asks 7:1, so the old rule would have
rejected five of the six on a bar their designers never aimed at. Nudging
the published colour along its own hue is what the script already does for
muted text, links and accents, and every shift is printed in the generated
CSS: Solarized light moves 4.13 to 7.07, Primer needed nothing at all.

Primer is named for the design system, not for GitHub. The colour values
are MIT; the name and the logo are trademarks, and NOTICE says plainly
that nothing here is endorsed.

The picker grid already wrapped on its own, so twelve cards needed no
layout change.

NOTICE

@@ -5,7 +5,7 @@ other people that ships inside it and the terms it comes under.
 
 ## Colour palettes
 
-Four of the palettes offered in Settings › Appearance are the work of their own
+Ten of the palettes offered in Settings › Appearance are the work of their own
 projects and are used under the MIT licence. Only the published colour values
 are used — no code, and nothing from anyone else's reimplementation of them.
 The values as fetched from each project are recorded in
@@ -35,9 +35,47 @@ Licensed under the MIT licence. The light variant is "Dawn".
 Copyright (c) 2019 enkia — https://github.com/enkia/tokyo-night-vscode-theme
 Licensed under the MIT licence. The light variant is "Day".
 
+### Catppuccin
+
+Copyright (c) 2021 Catppuccin — https://github.com/catppuccin/palette
+Licensed under the MIT licence. "Mocha" is the dark variant and "Latte" the
+light one; both are published in that repository's palette.json.
+
+### Solarized
+
+Copyright (c) 2011 Ethan Schoonover — https://github.com/altercation/solarized
+Licensed under the MIT licence. Light and dark are both original to it, and
+share one set of accent values by design.
+
+### Ayu
+
+Copyright (c) Konstantin Pschera — https://github.com/ayu-theme/ayu-colors
+Licensed under the MIT licence. The two signature accent colours come from the
+same author's ayu-theme/vscode-ayu, also MIT.
+
+### Kanagawa
+
+Copyright (c) 2021 Tommaso Laurenzi — https://github.com/rebelot/kanagawa.nvim
+Licensed under the MIT licence. "Wave" is the dark variant and "Lotus" the
+light one. The theme takes its name from Hokusai's print.
+
+### Everforest
+
+Copyright (c) 2019 Sainnhe Park — https://github.com/sainnhe/everforest
+Licensed under the MIT licence. The medium-contrast variant of each mode is
+the one used here.
+
+### Primer
+
+Copyright (c) GitHub, Inc. — https://github.com/primer/primitives
+Licensed under the MIT licence, which covers the colour values. "GitHub" and
+the Invertocat logo are trademarks of GitHub, Inc.; this palette is named
+"Primer" after the design system and is neither affiliated with nor endorsed
+by GitHub.
+
 ---
 
-The MIT licence, under which all four are used:
+The MIT licence, under which all ten are used:
 
     Permission is hereby granted, free of charge, to any person obtaining a
     copy of this software and associated documentation files (the "Software"),