🎨 Palette: Add ARIA labels to icon-only buttons

[thirdeyenation]

💡 What: Added aria-labels to icon-only buttons (zoom controls, delete buttons) across several modals and settings panels (webui/components/modals/image-viewer/image-viewer.html, webui/components/plugins/plugin-configs.html, webui/components/settings/skills/list.html, webui/components/plugins/toggle/plugin-toggles.html), and added aria-hidden="true" to their internal icon spans.
🎯 Why: Screen reader users could not identify the purpose of these buttons because they only contained ligature text like "zoom_in" or "delete", which is inaccessible.
📸 Before/After: Code-only change, UI looks identical. Tooltips added to zoom buttons for sighted users.
♿ Accessibility: Improves screen reader accessibility by providing clear textual labels for icon-only actions and hiding the visual-only icon text from assistive tech.

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PR created automatically by Jules for task 496654404977591302 started by @thirdeyenation

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