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/README.md

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+# Ferese theme
+
+The shared native UI theme for the shell, settings, lock screen, authentication
+prompt and screen-sharing/recording chooser.
+
+- `Palette` resolves KDL colors and corners and builds the native toolkit theme.
+- `PRESETS` defines the six built-in color schemes.
+- `font` and `text` share bounded font-name storage and explicit font selection.
+- `controls` supplies surfaces, navigation, buttons and input styles.
+- `menus` supplies headings, rows, sections, separators, switches and slider styles.
+- `calendar` supplies date/time labels, stacked clock digits and calendar grids.
+  Callers supply the date and navigation controls.
+- `icons` owns the shared SVG assets, outline icons, sizing and semantic tinting.
+- Contrast helpers keep filled controls readable in every interaction state.
+- `material::ModalMaterial` attaches a dialog to the compositor's shell material.
+  Keep the attachment alive with its window and make the client background
+  transparent after attachment succeeds. Other compositors retain the client fill.
+
+Applications own layout, data, actions and animation timing. Pass their current
+palette and animation progress into the shared components; do not build another
+native theme or copy a common control style into an application.
+
+```rust
+let palette = ferese_theme::Palette::from_document(Some(&document));
+let native_theme = palette.native_theme();
+let input_style = ferese_theme::controls::settings_input(palette);
+let font = ferese_theme::font(Some("Inter"));
+let label = ferese_theme::text("Appearance", font);
+```
+
+The compositor owns backdrop blur and material rendering. This crate does not
+provide a client-side imitation of those effects.