feat(themes): Omarchy catalog, 12 light themes, Dark/Light Appearance picker

Expand the catalog from 11 themes (10 dark, 1 light) to 37 (24/13):
all 18 remaining Omarchy defaults (palettes from each theme's
colors.toml) plus 8 canonical light themes (Tokyo Night Day, Solarized
Light, One Light, Ayu Light, GitHub Light, Gruvbox Light, Everforest
Light, Kanagawa Lotus). Lupine leads the light list as the default
light theme; the app default stays tokyo-night.

Appearance panel: Dark/Light segmented filter (SSR-initialized from the
user's current theme), scrollable theme list, Bookshelf section pinned;
active row revealed on open. Light themes carry color-scheme: light and
the soft-shadow token set. Public-page theme selects get Dark/Light
optgroups. New moon/sun icons.

tailwind.config: safelist the new theme ids — Tailwind v3 purges custom
@layer base class selectors that appear in no scanned content file, so
an unsafelisted id silently ships without its CSS (found the hard way).

theme.ts: applyTheme now swaps only theme-* classes (changing theme
from the login select no longer wipes min-h-screen) and keeps the class
in sync on <html> for the new ThemeFlashGuard — a pre-paint inline
script on the four public pages that applies the saved theme before
first paint.

Kanagawa's UI accent uses crystalBlue (#7e9cd8) instead of Omarchy's
foreground-as-accent so links stay distinguishable from text.

web/src/header.ts

@@ -5,6 +5,7 @@ import {
   changeTheme,
   changeWoodPaneling,
   loadWoodPaneling,
+  revealCurrentTheme,
   updateWoodPanelingIndicators,
 } from "./theme";
 import { getSelectedLibrary } from "./storage";
@@ -118,6 +119,7 @@ Alpine.data("header", () => ({
   changeTheme,
   changeWoodPaneling,
   loadWoodPaneling,
+  revealCurrentTheme,
   updateWoodPanelingIndicators,
   restoreLibrarySelection,
   initializeScanListener,