feat(api): add persistent file management helpers to frontend api module

Adds UserFile/UserFileDetail types plus apiListFiles, apiGetFileDetails,
apiUploadUserFiles, apiDeleteUserFiles, getFileThumbnailUrl, and
getFileDownloadUrl to support the Files page.

apps/web/src/lib/api.ts

@@ -80,6 +80,82 @@ export function getDownloadUrl(jobId: string, filename: string): string {
   return `/api/v1/download/${jobId}/${filename}`;
 }
 
+// ── Persistent File Management ──────────────────────────────────
+
+export interface UserFile {
+  id: string;
+  originalName: string;
+  mimeType: string;
+  size: number;
+  width: number | null;
+  height: number | null;
+  version: number;
+  toolChain: string[];
+  createdAt: string;
+}
+
+export interface UserFileDetail extends UserFile {
+  versions: Array<{
+    id: string;
+    version: number;
+    size: number;
+    toolChain: string[];
+    createdAt: string;
+  }>;
+}
+
+export async function apiListFiles(params?: {
+  search?: string;
+  limit?: number;
+  offset?: number;
+}): Promise<{ files: UserFile[]; total: number }> {
+  const searchParams = new URLSearchParams();
+  if (params?.search) searchParams.set("search", params.search);
+  if (params?.limit) searchParams.set("limit", String(params.limit));
+  if (params?.offset) searchParams.set("offset", String(params.offset));
+  const qs = searchParams.toString();
+  return apiGet(`/v1/files${qs ? `?${qs}` : ""}`);
+}
+
+export async function apiGetFileDetails(id: string): Promise<UserFileDetail> {
+  return apiGet(`/v1/files/${id}`);
+}
+
+export async function apiUploadUserFiles(
+  files: File[],
+): Promise<{ files: Array<{ id: string; originalName: string; size: number; version: number }> }> {
+  const formData = new FormData();
+  files.forEach((f) => formData.append("files", f));
+  const res = await fetch("/api/v1/files/upload", {
+    method: "POST",
+    headers: { Authorization: `Bearer ${getToken()}` },
+    body: formData,
+  });
+  if (!res.ok) throw new Error(`Upload failed: ${res.status}`);
+  return res.json();
+}
+
+export async function apiDeleteUserFiles(ids: string[]): Promise<{ deleted: number }> {
+  const res = await fetch("/api/v1/files", {
+    method: "DELETE",
+    headers: {
+      "Content-Type": "application/json",
+      Authorization: `Bearer ${getToken()}`,
+    },
+    body: JSON.stringify({ ids }),
+  });
+  if (!res.ok) throw new Error(`Delete failed: ${res.status}`);
+  return res.json();
+}
+
+export function getFileThumbnailUrl(id: string): string {
+  return `/api/v1/files/${id}/thumbnail`;
+}
+
+export function getFileDownloadUrl(id: string): string {
+  return `/api/v1/files/${id}/download`;
+}
+
 export async function apiDownloadBlob(
   jobId: string,
   filename: string,