feat(theme): per-app accent: pm gives window manifest accent before app runs (display ACCENT, refused after BUFFER); theme::with_accent keeps hue, shifts lightness until contrast passes, else theme accent; tally pink

docs/apps.md

@@ -72,7 +72,8 @@ required = ["display"]      # cannot work without; denied = not installed
 optional = []               # works without; the user decides each
 
 [appearance]
-accent = "#e91e63"          # optional: checked for format here, contrast by K-UI
+accent = "#e91e63"          # optional: its primary buttons and active states;
+                            # the display adapts its lightness to each theme
 ```
 
 The subset: `[table]` headers, `key = "string"`, `key = ["a", "b"]` on one