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/wifi-medium.svg

@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 60 60" role="img" aria-label="Wifi">
+<g transform="translate(3 -1.5) scale(0.9)">
+<circle cx="30" cy="53" r="3" fill="#3d7be6"/>
+<path d="M21,44 Q30,34 39,44" fill="none" stroke="currentColor" stroke-width="5" stroke-linecap="round"/>
+<path d="M12,35 Q30,15 48,35" fill="none" stroke="currentColor" stroke-width="5" stroke-linecap="round"/>
+<path opacity="0.25" d="M3,26 Q30,5 57,26" fill="none" stroke="currentColor" stroke-width="5" stroke-linecap="round"/>
+</g>
+</svg>