feat: wire file explorer to real backend API

Co-Authored-By: Claude <noreply@anthropic.com>

web/src/lib/api/files.ts

@@ -0,0 +1,64 @@
+import { useQuery, type UseQueryResult } from "@tanstack/react-query";
+
+import { apiClient } from "@/lib/api/client";
+
+export interface FileEntry {
+  name: string;
+  path: string;
+  isDir: boolean;
+  size?: number;
+  modTime?: string;
+  language?: string;
+}
+
+const LANGUAGE_BY_EXTENSION: Record<string, string> = {
+  css: "css",
+  go: "go",
+  html: "html",
+  js: "javascript",
+  jsx: "javascript",
+  json: "json",
+  md: "markdown",
+  py: "python",
+  ts: "typescript",
+  tsx: "typescript",
+  yaml: "yaml",
+  yml: "yaml",
+};
+
+export function inferLanguage(name: string): string | undefined {
+  const ext = name.split(".").pop()?.toLowerCase();
+  return ext ? LANGUAGE_BY_EXTENSION[ext] : undefined;
+}
+
+function fileListQueryKey(workspaceId: string, path: string) {
+  return ["workspaces", workspaceId, "files", path || "."] as const;
+}
+
+async function fetchFileList(
+  workspaceId: string,
+  path: string,
+): Promise<FileEntry[]> {
+  const queryPath = path || ".";
+  const url =
+    `/api/workspaces/${encodeURIComponent(workspaceId)}/files?` +
+    new URLSearchParams({ path: queryPath }).toString();
+  const res = await apiClient(url);
+  if (!res.ok) {
+    throw new Error(`Failed to list files: ${res.status}`);
+  }
+  return (await res.json()) as FileEntry[];
+}
+
+export function useFileList(
+  workspaceId: string | null,
+  path: string,
+  enabled = true,
+): UseQueryResult<FileEntry[], Error> {
+  const queryPath = path || ".";
+  return useQuery({
+    queryKey: fileListQueryKey(workspaceId ?? "", queryPath),
+    queryFn: () => fetchFileList(workspaceId!, queryPath),
+    enabled: !!workspaceId && enabled,
+  });
+}