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/assets/icons/status/record-saving.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 60 60" role="img" aria-label="Saving recording"><circle cx="30" cy="30" r="22" fill="none" stroke="currentColor" stroke-width="3"/><g fill="#3d7be6"><circle cx="20" cy="30" r="3"/><circle cx="30" cy="30" r="3"/><circle cx="40" cy="30" r="3"/></g></svg>