chore(palettes): remove dead per-palette files

Two clusters of palette-tree dead surface:

(1) themes/palettes/{flexoki-light,lumon,retro-82,rose-pine}/apps/
chromium.theme — 9-byte comma-separated RGB strings that no script
or Nix module reads. Chromium theming is driven by managed policies
in core/system/browser.nix (BrowserThemeColor / BrowserColorScheme
derived from the active palette's base00 + light-mode flag), not by
per-palette files. The chromium.theme files were vestigial from an
earlier chromium-theming mechanism.

(2) themes/palettes/summer-day/apps/kitty/{kitty.conf,everforest-
light.conf} — a 76KB stray kitty config in a nested apps/kitty/
subdirectory. features/apps/kitty/config/kitty.conf includes
~/.config/nomarchy/current/theme/kitty.conf (root of theme dir, not
under apps/), and themes/engine/files.nix now generates that file
from the active palette's base16 colors (commit 8d3ce2d). So the
summer-day file was at the wrong path AND superseded by the
generator.

`nix flake check --no-build` passes.

themes/palettes/rose-pine/apps/chromium.theme

@@ -1 +0,0 @@
-210,196,219