feat(themes): add Boreal + make theme appearance per-theme

Boreal — a Nord × Everforest × Dracula dark theme: a boreal forest at
night under the aurora. Nord's frost bones, Everforest's comfort, Dracula's
jewel-tone violet/cyan as the aurora light.

Palette (WCAG-checked, all 24 themes × 7 pairings pass): frost-slate base,
soft-vivid violet accent (#B79BE8, 6.35 on base) + frost-cyan accentAlt
(#86C7C0, 7.84 AAA), sage-green/gold/coral semantics, text 10.66 AAA.

Bespoke, non-standard surfaces:
- Waybar whole-swap (jsonc + css): a floating "aurora frost" bar of three
  frosted-glass pills; launcher+clock left, workspaces centre, and the whole
  right side is ONE continuous pill — the system tray shares its glass with
  the status modules, no separators (the seamless-tray requirement). Full
  module set (parity). GeistMono.
- Rofi: a frosted list base (used by every menu), plus a 4×3 large-icon grid
  for the app launcher only.
- Typography GeistMono Nerd Font (57 MB, new); Iosevka was rejected at 1.1 GB.

Per-theme appearance (new): a preset now carries a full fonts+ui block, like
border, so a theme can ship a bespoke font / terminal opacity / border
thickness / rounding and a switch always replaces it — no leak into the next
theme (verified: boreal→everforest resets mono/rounding/opacity). All 23 other
presets get the current defaults (idempotent — zero visual change). Boreal
runs GeistMono + 0.90 terminal opacity + 3px borders + 12px rounding.

Grid launcher (new, backward-compatible): drun renders via `-theme launcher`;
HM writes ~/.local/share/rofi/themes/launcher.rasi which defaults to
`@import "custom.rasi"` (every other theme's launcher = its list, unchanged),
and a theme may override it (Boreal's grid). Text menus keep the base list.

Wallpaper: an original procedurally-generated aurora-over-treeline (ImageMagick),
palette-matched.

V1: nix flake check --no-build green; strict JSON on every preset; contrast
checker green; the real rofi binary parses the base rasi and resolves
`-theme launcher` + @import + grid overlay; end-to-end eval with boreal active
resolves the waybar whole-swap (tray in the right cluster), the rofi grid
launcher, and the bespoke fonts/opacity/geometry reaching nomarchy.theme, with
no cross-theme contamination. NOT done: on-screen render of the desktop
(V2/V3) and preview.png (deferred to on-hardware capture).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

themes/boreal/rofi.rasi

@@ -0,0 +1,116 @@
+/**
+ * Boreal — rofi whole-swap (themes/<slug>/rofi.rasi).
+ * The base theme: a frosted aurora panel used by every menu (and, as a
+ * list, the fallback launcher). The app launcher reshapes this into a
+ * grid via themes/boreal/launcher.rasi, which @imports this file. The
+ * `configuration {}` block is omitted on purpose — it comes from
+ * modules/home/rofi.nix. Element structure mirrors the generated theme
+ * so the theme-grid picker's per-invocation -theme-str still lays out.
+ */
+
+* {
+    base:      #21272F;
+    glassBg:   #21272FE6;
+    surface:   #303A46;
+    overlay:   #404D5C;
+    text:      #D3DAE0;
+    subtext:   #97A3B2;
+    muted:     #5E6A78;
+    accent:    #B79BE8;
+    accentAlt: #86C7C0;
+    accentSoft: #B79BE83B;
+    frostEdge: #86C7C05C;
+
+    font: "GeistMono Nerd Font 11";
+    background-color: transparent;
+    text-color: @text;
+}
+
+window {
+    background-color: @glassBg;
+    border: 1px;
+    border-color: @frostEdge;
+    border-radius: 14px;
+    width: 620px;
+    location: center;
+    anchor: center;
+    padding: 16px;
+}
+
+mainbox {
+    background-color: transparent;
+    children: [ inputbar, message, listview ];
+    spacing: 12px;
+}
+
+inputbar {
+    children: [ prompt, entry ];
+    background-color: @surface;
+    text-color: @text;
+    border-radius: 10px;
+    padding: 12px 16px;
+    spacing: 10px;
+}
+
+prompt { text-color: @accent; }
+
+entry {
+    text-color: @text;
+    cursor: text;
+    placeholder: "Search…";
+    placeholder-color: @muted;
+}
+
+listview {
+    background-color: transparent;
+    columns: 1;
+    lines: 8;
+    dynamic: true;
+    scrollbar: false;
+    spacing: 6px;
+    padding: 4px 0px 0px 0px;
+}
+
+element {
+    background-color: transparent;
+    text-color: @text;
+    orientation: horizontal;
+    border-radius: 10px;
+    padding: 10px 14px;
+    spacing: 12px;
+}
+
+element normal.normal,
+element alternate.normal {
+    background-color: transparent;
+}
+
+/* Selected row lifts on a soft aurora-violet wash. */
+element selected.normal {
+    background-color: @accentSoft;
+    text-color: @text;
+}
+
+element-icon {
+    background-color: transparent;
+    size: 30px;
+    cursor: inherit;
+}
+
+element-text {
+    background-color: transparent;
+    text-color: inherit;
+    highlight: bold;
+    vertical-align: 0.5;
+}
+
+message { padding: 0px; }
+
+textbox {
+    background-color: @surface;
+    text-color: @text;
+    border-radius: 10px;
+    padding: 10px 14px;
+}
+
+scrollbar { width: 0px; }