feat: allow loading mods without a Steam API key

Add fetchModFromUrl/fetchModFileFromUrl and accept a fileUrl query param on /items routes so the frontend can download saves directly from a search result's file_url, with no key required.

apps/web/src/stores/modStore.ts

@@ -4,26 +4,28 @@ import { fetchMod } from '../api';
 
 interface ModState {
   id: string | null;
+  fileUrl?: string;
   mod: TTSMod | null;
   loading: boolean;
   error: string | null;
-  load: (id: string) => Promise<void>;
+  load: (id: string, fileUrl?: string) => Promise<void>;
   clear: () => void;
 }
 
 export const useModStore = create<ModState>((set) => ({
   id: null,
+  fileUrl: undefined,
   mod: null,
   loading: false,
   error: null,
-  load: async (id) => {
-    set({ loading: true, error: null, id });
+  load: async (id, fileUrl) => {
+    set({ loading: true, error: null, id, fileUrl });
     try {
-      const mod = await fetchMod(id);
+      const mod = await fetchMod(id, fileUrl);
       set({ mod, loading: false });
     } catch (err) {
       set({ loading: false, error: String(err) });
     }
   },
-  clear: () => set({ id: null, mod: null, error: null, loading: false }),
+  clear: () => set({ id: null, fileUrl: undefined, mod: null, error: null, loading: false }),
 }));