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/notifications-off.svg

@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 60 60" role="img" aria-label="Notification off">
+<g transform="translate(0 -2)">
+<path d="M30,10 A16,16 0 0,1 46,26 L46,38 L14,38 L14,26 A16,16 0 0,1 30,10 Z" fill="currentColor" opacity="0.5"/>
+<rect x="10" y="38" width="40" height="5" rx="2" fill="currentColor" opacity="0.5"/>
+<circle cx="30" cy="50" r="4" fill="currentColor" opacity="0.5"/>
+<path d="M8,8 L52,56" fill="none" stroke="currentColor" stroke-width="5" stroke-linecap="round"/>
+</g>
+</svg>