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.

crates/pstr-app/src/theme.rs

@@ -84,26 +84,90 @@ impl Role {
         }
     }
 
+    /// Headings are set in the semibold cut; everything below them in the
+    /// regular one.
+    pub fn family(self) -> egui::FontFamily {
+        match self {
+            Self::Display | Self::Title | Self::Heading | Self::Section => semibold(),
+            _ => egui::FontFamily::Proportional,
+        }
+    }
+
     /// For the hand-painted parts, which lay text out through a `Painter` and
     /// never see a `RichText`.
     pub fn font(self) -> egui::FontId {
-        egui::FontId::proportional(self.size())
+        egui::FontId::new(self.size(), self.family())
     }
 
     /// For the parts that go through egui's widgets.
     pub fn rich(self, text: impl Into<String>) -> egui::RichText {
-        egui::RichText::new(text).size(self.size())
+        egui::RichText::new(text)
+            .size(self.size())
+            .family(self.family())
     }
 }
 
-/// Install a real CJK fallback before the default egui fonts.  egui ships a
-/// compact Latin font, but it intentionally does not bundle the multi-megabyte
-/// CJK families.  Native desktops already provide one, so use it when present.
+/// The UI typeface, bundled rather than taken from the system so a title
+/// sets the same on every desktop. Inter, under the OFL — the licence is
+/// beside the files.
+const INTER: &[u8] = include_bytes!("../assets/fonts/Inter-Regular.ttf");
+const INTER_SEMIBOLD: &[u8] = include_bytes!("../assets/fonts/Inter-SemiBold.ttf");
+
+/// The family the headings are set in. egui has no notion of weight, so the
+/// semibold cut is a family of its own.
+pub fn semibold() -> egui::FontFamily {
+    egui::FontFamily::Name("semibold".into())
+}
+
+/// Inter, the icon font, and egui's own fonts behind them for the emoji and
+/// symbols Inter does not carry. `cjk` goes last, when there is one.
+fn font_definitions(cjk: Option<egui::FontData>) -> egui::FontDefinitions {
+    use egui::FontFamily::{Monospace, Proportional};
+
+    let mut fonts = egui::FontDefinitions::default();
+    fonts
+        .font_data
+        .insert("inter".into(), Arc::new(egui::FontData::from_static(INTER)));
+    fonts.font_data.insert(
+        "inter-semibold".into(),
+        Arc::new(egui::FontData::from_static(INTER_SEMIBOLD)),
+    );
+    fonts
+        .families
+        .entry(Proportional)
+        .or_default()
+        .insert(0, "inter".into());
+    // Right behind Inter. The icons are in the private use area, so nothing
+    // Inter has is shadowed by them.
+    egui_phosphor::add_to_fonts(&mut fonts, egui_phosphor::Variant::Regular);
+    if let Some(cjk) = cjk {
+        let name = "system-cjk-fallback".to_owned();
+        fonts.font_data.insert(name.clone(), Arc::new(cjk));
+        for family in [Proportional, Monospace] {
+            fonts.families.entry(family).or_default().push(name.clone());
+        }
+    }
+    let fallbacks = fonts.families[&Proportional]
+        .iter()
+        .filter(|name| *name != "inter")
+        .cloned();
+    let semibold_chain = std::iter::once("inter-semibold".to_owned())
+        .chain(fallbacks)
+        .collect();
+    fonts.families.insert(semibold(), semibold_chain);
+    fonts
+}
+
+/// Install the bundled fonts now, and a CJK fallback when the system has one.
 ///
-/// On a thread of its own: `fc-match` and reading a font file of tens of
-/// megabytes held the first frame back by a visible moment, and every name
-/// that needs the fallback is still loading from the catalog by then anyway.
-pub fn install_font_fallbacks(ctx: &egui::Context) {
+/// The bundled ones are compiled in and cost nothing to hand over. The CJK
+/// fallback is on a thread of its own: `fc-match` and reading a font file of
+/// tens of megabytes held the first frame back by a visible moment, and every
+/// name that needs the fallback is still loading from the catalog by then
+/// anyway. egui deliberately does not bundle the multi-megabyte CJK families,
+/// and native desktops already provide one.
+pub fn install_fonts(ctx: &egui::Context) {
+    ctx.set_fonts(font_definitions(None));
     let ctx = ctx.clone();
     let spawned = std::thread::Builder::new()
         .name("fonts".into())
@@ -120,16 +184,9 @@ fn install_cjk_fallback(ctx: &egui::Context) {
     let Ok(bytes) = std::fs::read(path) else {
         return;
     };
-
-    let mut fonts = egui::FontDefinitions::default();
     let mut data = egui::FontData::from_owned(bytes);
     data.index = index;
-    let name = "system-cjk-fallback".to_owned();
-    fonts.font_data.insert(name.clone(), Arc::new(data));
-    for family in [egui::FontFamily::Proportional, egui::FontFamily::Monospace] {
-        fonts.families.entry(family).or_default().push(name.clone());
-    }
-    ctx.set_fonts(fonts);
+    ctx.set_fonts(font_definitions(Some(data)));
     ctx.request_repaint();
 }