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

docs/testing.md

@@ -406,6 +406,57 @@ reachable by a test:
 - the group's member check (`!` deleted), which agrees on every account
   whose own group lists no members, the usual case.
 
+## Viewer color schemes (2026-10-19)
+
+`ledger-gui/src/schemes.rs` (docs/color-schemes.md). No mutation run (the
+viewer's rule); its two musts are tested directly instead:
+- `schemes::painted::every_scheme_paints_the_same_words_and_figures_readably`
+  draws thirteen pages (an entry, the company, assets, documents, overview,
+  cash, profit, transactions, the P&L, the balance sheet, accounts,
+  parties, the journal) in all 80 schemes, a thread a page, and reads what
+  was painted where it can be seen: every run of text, report rows
+  included, is the same and in the same place in every scheme, and each is
+  at 4.5:1 or better against what was painted under it by then (the fills
+  in paint order, cut to their clips, translucent ones laid over what was
+  below; every section of a text, its own color or the fallback). It found
+  egui's placeholder text (its weak text, 60% alpha of the text) at 2.8:1.
+  Not painted by it: hover, selection and new-entry rows, tooltips and
+  the menu, whose grounds the palette tests check by arithmetic.
+- `the_system_turning_light_or_dark_changes_nothing`: starting as eframe
+  does (following the system), a scheme chosen and the system then
+  flipped leaves every painted color as it was. It fails on the first
+  version, which set only the current theme's style.
+- The palette tests check every scheme: every text color at 4.5:1 on
+  every ground (soft fills included), text over secondary over faint each
+  at least 1.2 times the contrast of the next on its worst ground, chart
+  series at 3:1 on cards and the hover tint, the charts' three series shown
+  together and gains, losses and text each ΔE 20 or more apart, the
+  logo's initial readable on the accent, light or dark as its background
+  is, and the filter showing exactly its mode; the menu test chooses,
+  filters and keeps a scheme, and its accessible labels check only the
+  family in force and select the variant in force; `app::tests` restores
+  the scheme (and the old light/dark choice) from the preferences.
+
+The first version's review (2026-10-19) found figures turning unreadable
+when the system's theme flipped, Ayu and the families after it out of
+reach in a short window, Income and Net the same color in twelve schemes,
+pills, faint figures and the logo initial below 4.5:1, a new-entry tint
+that bleached reds and greens, and a "same figures" test that compared
+only accessibility labels (no report rows); all fixed, with the tests
+above. Round 2 found secondary and faint text made alike by lifting each
+alone (identical in Wanderbooks Light), the painted test picking a text's
+ground without paint order or clips, and every family's accessible label
+carrying the hidden check; fixed, with the tests above. The owner, trying
+it (2026-10-19): Ayu out of reach (the family list scrolled inside the
+menu, its scroll bar hidden), the families not alphabetical, and a click on
+a variant's colors doing nothing. Now the families are alphabetical, in
+columns with no scrolling, and a variant's whole row is its button;
+`every_family_is_on_screen_in_order_and_a_whole_row_chooses` checks all
+three in a tall window and a short one. Earlier: the viewer's own light palette's green below 4.5:1 on the
+sidebar (4.35:1), and a first fix (moving colors toward the text color)
+that turned Everforest's red and green into the same grey; colors keep
+their hue and change only lightness.
+
 ## Benchmarks (baseline 2026-10-13)
 
 No budget, by decision (Stephen, 2026-10-13: the books do little work