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/test/hooks/useShare.test.ts

@@ -14,7 +14,7 @@ describe("useShare", () => {
 		mockAlert = vi.fn();
 		global.alert = mockAlert;
 
-		mockClipboard = { writeText: vi.fn() };
+		mockClipboard = { writeText: vi.fn().mockResolvedValue(undefined) };
 		Object.defineProperty(navigator, "clipboard", {
 			value: mockClipboard,
 			writable: true,
@@ -237,7 +237,7 @@ describe("useShare", () => {
 			result.current.setShareLink("http://localhost:5173/share/test-token");
 		});
 
-		act(() => {
+		await act(async () => {
 			result.current.copyShareLink();
 		});