refactor(frontend): add SVG schema to network schema (#3875)

# Motivation

As suggested in the past, we should refine the schema of network type to
be more specific for the icons.

src/frontend/src/lib/schema/network.schema.ts

@@ -17,11 +17,15 @@ export const NetworkAppMetadataSchema = z.object({
 	explorerUrl: UrlSchema
 });
 
+const IconSchema = z
+	.string()
+	.refine((value) => value.endsWith('.svg'), { message: 'Must be an SVG file' });
+
 export const NetworkSchema = z.object({
 	id: NetworkIdSchema,
 	env: NetworkEnvironmentSchema,
 	name: z.string(),
-	icon: z.string().optional(),
-	iconBW: z.string().optional(),
+	icon: IconSchema.optional(),
+	iconBW: IconSchema.optional(),
 	buy: z.custom<AtLeastOne<NetworkBuy>>().optional()
 });

src/frontend/src/tests/lib/schema/network.schema.spec.ts

@@ -86,8 +86,8 @@ describe('network.schema', () => {
 
 		const validNetwork = {
 			...validNetworkWithRequiredFields,
-			icon: 'https://example.com/icon.png',
-			iconBW: 'https://example.com/icon-bw.png',
+			icon: 'https://example.com/icon.svg',
+			iconBW: 'https://example.com/icon-bw.svg',
 			buy: { onramperId: 'icp' }
 		};
 
@@ -115,5 +115,21 @@ describe('network.schema', () => {
 			const { name: _, ...invalidNetwork } = validNetwork;
 			expect(() => NetworkSchema.parse(invalidNetwork)).toThrow();
 		});
+
+		it('should fail validation when icon is not a valid SVG string', () => {
+			const invalidNetwork = {
+				...validNetwork,
+				icon: 'https://example.com/invalid-icon.png'
+			};
+			expect(() => NetworkSchema.parse(invalidNetwork)).toThrow();
+		});
+
+		it('should fail validation when iconBW is not a valid SVG string', () => {
+			const invalidNetwork = {
+				...validNetwork,
+				iconBW: 'https://example.com/invalid-icon-bw.png'
+			};
+			expect(() => NetworkSchema.parse(invalidNetwork)).toThrow();
+		});
 	});
 });