Share native theme components and fix dialog backdrop blur

Centralize native palettes, presets, typography, controls, menus, calendar rendering, and icon assets in ferese-theme. Reuse the shared components across the shell, settings, lock screen, authentication prompt, and screen-sharing chooser.

Attach themed dialogs to compositor-owned materials, correct backdrop capture and sampling across output transforms, smooth patterned backgrounds, and prevent clipped picker buttons with the configured shell font.

crates/ferese-theme/src/typography.rs

@@ -0,0 +1,30 @@
+use std::{
+    collections::HashMap,
+    sync::{Mutex, OnceLock},
+};
+
+pub fn font(family: Option<&str>) -> cosmic::font::Font {
+    let Some(family) = family else {
+        return cosmic::font::default();
+    };
+    static FONTS: OnceLock<Mutex<HashMap<String, cosmic::font::Font>>> = OnceLock::new();
+    let mut fonts = FONTS.get_or_init(Default::default).lock().unwrap();
+    if let Some(font) = fonts.get(family) {
+        return *font;
+    }
+    if fonts.len() >= 64 {
+        return cosmic::font::default();
+    }
+    let name = Box::leak(family.to_owned().into_boxed_str());
+    let font = cosmic::font::Font::with_name(name);
+    fonts.insert(family.to_owned(), font);
+    font
+}
+
+/// COSMIC's text helper overrides Settings::default_font; set the Ferese font explicitly.
+pub fn text<'a>(
+    content: impl Into<std::borrow::Cow<'a, str>> + 'a,
+    font: cosmic::font::Font,
+) -> cosmic::widget::Text<'a, cosmic::Theme, cosmic::Renderer> {
+    cosmic::widget::text(content).font(font)
+}