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.

tailwind.config.ts

@@ -18,6 +18,36 @@ const config: Config = {
     "theme-catppuccin-macchiato",
     "theme-catppuccin-frappe",
     "theme-catppuccin-latte",
+    // Omarchy dark themes (theme_options.go). Theme ids are runtime values
+    // applied via `theme-<name>` classes, so each must be safelisted or the
+    // CSS build purges its variable block from @layer base.
+    "theme-vantablack",
+    "theme-last-horizon",
+    "theme-ethereal",
+    "theme-hackerman",
+    "theme-matte-black",
+    "theme-solitude",
+    "theme-retro-82",
+    "theme-osaka-jade",
+    "theme-kanagawa",
+    "theme-miasma",
+    "theme-lumon",
+    "theme-ristretto",
+    "theme-gruvbox",
+    "theme-everforest",
+    // Light themes
+    "theme-tokyo-night-day",
+    "theme-solarized-light",
+    "theme-one-light",
+    "theme-ayu-light",
+    "theme-github-light",
+    "theme-gruvbox-light",
+    "theme-everforest-light",
+    "theme-kanagawa-lotus",
+    "theme-rose-pine",
+    "theme-lupine",
+    "theme-flexoki-light",
+    "theme-white",
   ],
   theme: {
     extend: {