feat(app): bundled Inter and Phosphor icons, window icon

Headings are set in Inter SemiBold, everything else in Inter Regular, so a
title sets the same on every desktop. Media and navigation glyphs (⏭, 🔊, ⛶,
★) come from the Phosphor icon font instead of whichever fallback font had
them. The CJK fallback still loads on its own thread and now joins the
bundled fonts instead of replacing them. The window carries the app icon
on X11 and Windows.

docs/DESIGN-TOKENS.md

@@ -35,8 +35,16 @@ screen and not for anything in a library grid).
 | Caption | 12 | context rather than content: counts, sizes, errors under a field |
 | Micro | 11 | the smallest thing that stays legible — a badge over artwork |
 
-Weight and leading are each side's own: egui has one weight, and Compose derives
-line height as 1.35 × size rather than naming it nine more times.
+Weight and leading are each side's own. The desktop bundles Inter
+(`pstr-app/assets/fonts`, OFL) and sets Display, Title, Heading and Section in
+its semibold cut, which egui sees as a family of its own (`theme::semibold`);
+everything below Section is the regular cut. Compose derives line height as
+1.35 × size rather than naming it nine more times.
+
+Icons on the desktop come from the Phosphor icon font (`egui-phosphor`,
+regular weight), installed right behind Inter so an icon can sit inside an
+ordinary label. Do not use Unicode symbols such as ⏭ or 🔊 as icons: they come
+out of whichever fallback font has them, at that font's size and baseline.
 
 Both clients point their framework's *default* styles at the ramp — egui's five
 `TextStyle`s, Compose's fifteen — so a stock widget nobody restyled still lands