colours from the wallpaper through matugen

- matugen/amane.colors: a matugen template (primary, on_primary,
  primary_container, primary_fixed, on_surface, on_surface_variant,
  outline_variant, surface_container high/normal/lowest) that skwd-wall
  renders into ~/.config/amane/theme on every new wallpaper
- theme.rs: a Theme service reads that file and shell.conf twice a
  second (matugen replaces its output, which a file watch can lose) and
  fades all ten colours together on one Animation; without a theme file
  the shell keeps its pink on purple
- the island, the idle pill and the workspace pill draw with the theme;
  white overlays (chips, tracks, hover tints) stay as they are
- shell.conf: cover_colors (true: the open media card and equalizer take
  the cover's gradient as background, accents stay the wallpaper's) and
  transition_ms (0 switches instantly), both applied without a restart
- parse: settings() and rgb(), with a test (6 pass)
- checked on the desktop with a hand-written theme file: pill, workspace
  pill and card recolour, cover_colors switches the card background live

.gitignore

@@ -2,3 +2,6 @@
 Cargo.toml
 Cargo.lock
 target/
+
+# written by matugen (through skwd-wall) from the wallpaper, see matugen/amane.colors
+theme