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/button.rs

@@ -0,0 +1,53 @@
+use crate::{composite, foreground};
+use cosmic::{
+    iced::{Background, Color},
+    theme,
+    widget::button,
+};
+
+#[derive(Clone, Copy)]
+pub(crate) enum State {
+    Active,
+    Hovered,
+    Pressed,
+    Disabled,
+}
+
+pub(crate) fn accent_button_style(
+    theme: &cosmic::Theme,
+    state: State,
+    focused: bool,
+) -> button::Style {
+    let native = theme.cosmic();
+    let component = &native.accent_button;
+    let fill: Color = match state {
+        State::Active => component.base.into(),
+        State::Hovered => component.hover.into(),
+        State::Pressed => component.pressed.into(),
+        State::Disabled => Color {
+            a: 0.5,
+            ..component.base.into()
+        },
+    };
+    let background = composite(fill, native.primary(false).base.into());
+    let foreground = foreground(background, component.on.into());
+    button::Style {
+        background: Some(Background::Color(background)),
+        text_color: Some(foreground),
+        icon_color: Some(foreground),
+        border_radius: native.corner_radii.radius_xl.into(),
+        outline_width: if focused { 1. } else { 0. },
+        outline_color: foreground,
+        ..Default::default()
+    }
+}
+
+/// Filled accent buttons and selected rows share this per-state contrast policy.
+pub fn accent_button() -> theme::Button {
+    theme::Button::Custom {
+        active: Box::new(|focused, theme| accent_button_style(theme, State::Active, focused)),
+        hovered: Box::new(|focused, theme| accent_button_style(theme, State::Hovered, focused)),
+        pressed: Box::new(|focused, theme| accent_button_style(theme, State::Pressed, focused)),
+        disabled: Box::new(|theme| accent_button_style(theme, State::Disabled, false)),
+    }
+}