fix: harden extension security and plugin reliability

Address audit findings across background handlers, openers,
plugins, and UI: URL allowlists, XSS reductions, popup lifecycle
fixes, plugin dispose/cleanup, cloud sync hardening, global search
mathjs sandbox, and settings storage fixes.

src/interface/components/Slider.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-  let { state, onChange, min = 0, max = 100, step = 1 } = $props<{ 
+  let { state = $bindable(), onChange, min = 0, max = 100, step = 1 } = $props<{ 
     state: number, 
     onChange: (value: number) => void,
     min?: number,