viewer: color schemes, twenty families and every variant, with a light/dark filter

Owner, 2026-10-19: full color-scheme support for the viewer, the top
Neovim-style schemes, about twenty families each with a flyout of all its
variants, a light/dark/all filter, Ayu included, alphabetical, a whole row
to click.

- The sidebar's corner button (the light/dark toggle before) opens the
  menu: the filter, then, alphabetically and all on screen at once (in
  columns in a short window), Ayu, Catppuccin, Cyberdream, Dracula,
  Everforest, GitHub, Gruvbox, Kanagawa, Material, Melange, Monokai Pro,
  Night Owl, Nightfox, Nord, One Dark, Oxocarbon, Rosé Pine, Solarized,
  Sonokai, Tokyo Night and Wanderbooks (the viewer's own Light and Dark):
  80 schemes, each variant a row with a strip of its colors.
- Colors from each scheme's official source, checked value by value
  (docs/color-schemes.md; the table names the sources).
- Every palette, the viewer's own included, keeps every text color
  (figures, gains and losses, warnings, links, secondary and faint text)
  at WCAG AA (4.5:1) on every ground it sits on, soft fills included; a
  color that falls short keeps its hue and only changes lightness. Text,
  secondary and faint text stay apart (each 1.2 times the next), gains,
  losses and text and the charts' series shown together stay plainly
  different (CIE76 ΔE 20).
- The scheme sets both egui styles and pins its mode, so the system
  turning light or dark changes nothing (it made figures unreadable).
- Preferences now live in the platform's place for app settings
  ($XDG_CONFIG_HOME/wanderbooks-viewer on Linux), not eframe's default,
  which was $XDG_DATA_HOME/wanderbooks: the data root's own place. The
  old file is moved once.
- Tests: every page of thirteen painted in all 80 schemes, the same words
  in the same places, each text readable on what was painted under it;
  the menu's order, reach and whole-row clicks in a tall and a short
  window; the system flip; preferences restored. Two review rounds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-gui/src/theme.rs

@@ -1,5 +1,5 @@
-//! Look and feel: one palette per mode, Inter with tabular figures, and
-//! the spacing the whole app shares.
+//! Look and feel: the palette of the color scheme in force (schemes.rs),
+//! Inter with tabular figures, and the spacing the whole app shares.
 
 use egui::{
     Color32, Context, CornerRadius, FontData, FontDefinitions, FontFamily, FontId, Margin, Stroke,
@@ -90,13 +90,16 @@ pub const DARK: Palette = Palette {
     ],
 };
 
-/// The palette for the current mode.
-pub fn pal(ctx: &Context) -> &'static Palette {
-    if ctx.global_style().visuals.dark_mode {
-        &DARK
-    } else {
-        &LIGHT
-    }
+/// Where the palette in force is kept, in the context's memory.
+fn palette_id() -> egui::Id {
+    egui::Id::new("wanderbooks-palette")
+}
+
+/// The palette in force: the scheme's that `apply` set, else the
+/// viewer's own for the current mode.
+pub fn pal(ctx: &Context) -> Palette {
+    ctx.data(|d| d.get_temp::<Palette>(palette_id()))
+        .unwrap_or_else(|| crate::schemes::own(ctx.global_style().visuals.dark_mode).palette())
 }
 
 pub const SEMIBOLD: &str = "semibold";
@@ -166,9 +169,18 @@ pub fn install_fonts(ctx: &Context) {
     ctx.set_fonts(fonts);
 }
 
-/// Apply the app's style for light or dark mode.
+/// Apply the viewer's own style for light or dark mode (tests).
+#[cfg(test)]
 pub fn apply(ctx: &Context, dark: bool) {
-    let p = if dark { &DARK } else { &LIGHT };
+    apply_scheme(ctx, crate::schemes::own(dark));
+}
+
+/// Apply a color scheme: its palette, everywhere.
+pub fn apply_scheme(ctx: &Context, scheme: &crate::schemes::Scheme) {
+    let dark = scheme.dark;
+    let palette = scheme.palette();
+    ctx.data_mut(|d| d.insert_temp(palette_id(), palette));
+    let p = &palette;
     let mut visuals = if dark {
         Visuals::dark()
     } else {
@@ -179,6 +191,9 @@ pub fn apply(ctx: &Context, dark: bool) {
     visuals.extreme_bg_color = p.surface;
     visuals.faint_bg_color = p.hover;
     visuals.override_text_color = Some(p.text);
+    // egui's weak text (placeholders, hints) is the text at 60% alpha
+    // unless set: the palette's secondary text, which is kept readable.
+    visuals.weak_text_color = Some(p.muted);
     visuals.hyperlink_color = p.accent;
     visuals.selection.bg_fill = p.selected;
     visuals.selection.stroke = Stroke::new(1.0, p.accent);
@@ -207,7 +222,21 @@ pub fn apply(ctx: &Context, dark: bool) {
     visuals.widgets.active.bg_fill = p.selected;
     visuals.widgets.active.weak_bg_fill = p.selected;
     visuals.widgets.active.fg_stroke = Stroke::new(1.0, p.text);
-    ctx.set_visuals(visuals);
+    visuals.widgets.open.bg_fill = p.hover;
+    visuals.widgets.open.weak_bg_fill = p.hover;
+    visuals.widgets.open.bg_stroke = Stroke::new(1.0, p.border);
+    visuals.widgets.open.fg_stroke = Stroke::new(1.0, p.text);
+    // egui keeps a light and a dark style and paints with the one its
+    // theme picks, which follows the system unless told: both get the
+    // scheme's visuals, and the theme is pinned to the scheme's mode, so
+    // a system that turns light or dark later changes nothing (review of
+    // the color schemes, 2026-10-19: figures went unreadable).
+    ctx.set_theme(if dark {
+        egui::Theme::Dark
+    } else {
+        egui::Theme::Light
+    });
+    ctx.all_styles_mut(|style| style.visuals = visuals.clone());
     ctx.all_styles_mut(|style| {
         style.text_styles = [
             (TextStyle::Heading, semibold(20.0)),