feat(frontend): add API client, layout, and routing

- Create Axios-based API client with sources, jobs, and dashboard endpoints
- Add responsive Layout component with navigation sidebar
- Set up React Router with Dashboard, Backups, and Settings routes
- Configure TanStack Query provider with default options
- Use lucide-react for navigation icons

frontend/node_modules/arg/index.d.ts

@@ -0,0 +1,44 @@
+declare function arg<T extends arg.Spec>(
+	spec: T,
+	options?: arg.Options
+): arg.Result<T>;
+
+declare namespace arg {
+	export const flagSymbol: unique symbol;
+
+	export function flag<T>(fn: T): T & { [arg.flagSymbol]: true };
+
+	export const COUNT: Handler<number> & { [arg.flagSymbol]: true };
+
+	export type Handler<T = any> = (
+		value: string,
+		name: string,
+		previousValue?: T
+	) => T;
+
+	export class ArgError extends Error {
+		constructor(message: string, code: string);
+
+		code: string;
+	}
+
+	export interface Spec {
+		[key: string]: string | Handler | [Handler];
+	}
+
+	export type Result<T extends Spec> = { _: string[] } & {
+		[K in keyof T]?: T[K] extends Handler
+			? ReturnType<T[K]>
+			: T[K] extends [Handler]
+			? Array<ReturnType<T[K][0]>>
+			: never;
+	};
+
+	export interface Options {
+		argv?: string[];
+		permissive?: boolean;
+		stopAtPositional?: boolean;
+	}
+}
+
+export = arg;