fix: logo optimization, deprecated meta tag, and clipboard copy fallback (#306)

- Replace 2 MB favicon.svg (base64-PNG-in-SVG) with optimized 43 KB app-logo.png (256x256)
- Update AppHeader and AboutModal references to use new logo
- Remove SVG favicon link from index.html (PNG/ICO favicons remain)
- Fix deprecated apple-mobile-web-app-capable → mobile-web-app-capable meta tag
- Add clipboard copy fallback for non-secure contexts (LAN IP over HTTP)

Closes #303

frontend/src/components/AppHeader.tsx

@@ -73,7 +73,7 @@ export function AppHeader({ onOpenProfile, onOpenAbout }: AppHeaderProps) {
 	return (
 		<header className="hero">
 			<div className="hero-title">
-				<img src="/favicon.svg" alt="MedAssist-ng" className="hero-logo" />
+				<img src="/app-logo.png" alt="MedAssist-ng" className="hero-logo" />
 				<div>
 					<p className="eyebrow">{pageInfo.eyebrow}</p>
 					<h1>{pageInfo.title}</h1>