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.

Cargo.toml

@@ -77,6 +77,9 @@ eframe = { version = "0.35", default-features = false, features = [
     "x11",
 ] }
 egui = "0.35"
+# The icons on buttons. Glyphs like ⏭ and 🔊 come out of whichever fallback
+# font has them, at its own size and baseline; an icon font is one set.
+egui-phosphor = { version = "0.13", default-features = false, features = ["regular"] }
 # Poster thumbnails only: Proton renders them as JPEG, and a decoder that also
 # pulls in every exotic format is weight this app has no use for.
 image = { version = "0.25", default-features = false, features = ["jpeg", "png", "webp"] }