feat(stores): add Zustand store for Files page state management

Implements useFilesPageStore with file listing, upload, bulk delete,
selection, checkbox management, search, and tab switching actions.

apps/web/src/stores/files-page-store.ts

@@ -0,0 +1,87 @@
+import { create } from "zustand";
+import {
+  apiListFiles,
+  apiUploadUserFiles,
+  apiDeleteUserFiles,
+  type UserFile,
+} from "@/lib/api";
+
+interface FilesPageState {
+  files: UserFile[];
+  total: number;
+  selectedFileId: string | null;
+  checkedIds: Set<string>;
+  activeTab: "recent" | "upload";
+  searchQuery: string;
+  loading: boolean;
+  error: string | null;
+
+  fetchFiles: () => Promise<void>;
+  uploadFiles: (files: File[]) => Promise<void>;
+  deleteChecked: () => Promise<void>;
+  selectFile: (id: string | null) => void;
+  toggleChecked: (id: string) => void;
+  toggleCheckAll: () => void;
+  setSearchQuery: (q: string) => void;
+  setActiveTab: (tab: "recent" | "upload") => void;
+}
+
+export const useFilesPageStore = create<FilesPageState>((set, get) => ({
+  files: [],
+  total: 0,
+  selectedFileId: null,
+  checkedIds: new Set(),
+  activeTab: "recent",
+  searchQuery: "",
+  loading: false,
+  error: null,
+
+  fetchFiles: async () => {
+    set({ loading: true, error: null });
+    try {
+      const { searchQuery } = get();
+      const result = await apiListFiles({ search: searchQuery || undefined, limit: 100 });
+      set({ files: result.files, total: result.total, loading: false });
+    } catch (err) {
+      set({ error: err instanceof Error ? err.message : "Failed to load files", loading: false });
+    }
+  },
+
+  uploadFiles: async (files) => {
+    set({ loading: true, error: null });
+    try {
+      await apiUploadUserFiles(files);
+      await get().fetchFiles();
+      set({ activeTab: "recent" });
+    } catch (err) {
+      set({ error: err instanceof Error ? err.message : "Upload failed", loading: false });
+    }
+  },
+
+  deleteChecked: async () => {
+    const { checkedIds } = get();
+    if (checkedIds.size === 0) return;
+    set({ loading: true, error: null });
+    try {
+      await apiDeleteUserFiles(Array.from(checkedIds));
+      set({ checkedIds: new Set(), selectedFileId: null });
+      await get().fetchFiles();
+    } catch (err) {
+      set({ error: err instanceof Error ? err.message : "Delete failed", loading: false });
+    }
+  },
+
+  selectFile: (id) => set({ selectedFileId: id }),
+  toggleChecked: (id) => {
+    const { checkedIds } = get();
+    const next = new Set(checkedIds);
+    if (next.has(id)) next.delete(id); else next.add(id);
+    set({ checkedIds: next });
+  },
+  toggleCheckAll: () => {
+    const { files, checkedIds } = get();
+    set({ checkedIds: checkedIds.size === files.length ? new Set() : new Set(files.map(f => f.id)) });
+  },
+  setSearchQuery: (q) => set({ searchQuery: q }),
+  setActiveTab: (tab) => set({ activeTab: tab }),
+}));