feat: add SPA, serve at /app/, update Dockerfile and README

- React + TanStack Router + shadcn/ui SPA under spa/
- serve spa/dist at /app/ with index.html fallback for client routing
- Dockerfile: node build stage for SPA, copy dist into runtime image
- README: document SPA, CORS_ORIGINS env var, architecture entry
- vite base set to /app/, manifest.json paths fixed

spa/src/hooks/use-imports.ts

@@ -0,0 +1,95 @@
+import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query"
+import {
+  applyMapping,
+  confirmImport,
+  createImportSession,
+  deleteImportProfile,
+  getImportPreview,
+  getImportProfiles,
+  getImportSession,
+  saveImportProfile,
+} from "@/lib/api/imports"
+import type {
+  ApplyMappingRequest,
+  ConfirmRequest,
+  SaveProfileRequest,
+} from "@/lib/api/imports"
+
+export const importKeys = {
+  session: (id: string) => ["import-session", id] as const,
+  preview: (id: string) => ["import-preview", id] as const,
+  profiles: ["import-profiles"] as const,
+}
+
+export function useImportPreview(id: string) {
+  return useQuery({
+    queryKey: importKeys.preview(id),
+    queryFn: () => getImportPreview(id),
+    enabled: !!id,
+  })
+}
+
+export function useCreateImportSession() {
+  return useMutation({
+    mutationFn: (file: File) => createImportSession(file),
+  })
+}
+
+export function useImportSession(id: string) {
+  return useQuery({
+    queryKey: importKeys.session(id),
+    queryFn: () => getImportSession(id),
+    enabled: !!id,
+  })
+}
+
+export function useApplyMapping() {
+  return useMutation({
+    mutationFn: ({
+      sessionId,
+      data,
+    }: {
+      sessionId: string
+      data: ApplyMappingRequest
+    }) => applyMapping(sessionId, data),
+  })
+}
+
+export function useConfirmImport() {
+  return useMutation({
+    mutationFn: ({
+      sessionId,
+      data,
+    }: {
+      sessionId: string
+      data: ConfirmRequest
+    }) => confirmImport(sessionId, data),
+  })
+}
+
+export function useImportProfiles() {
+  return useQuery({
+    queryKey: importKeys.profiles,
+    queryFn: getImportProfiles,
+  })
+}
+
+export function useSaveImportProfile() {
+  const qc = useQueryClient()
+  return useMutation({
+    mutationFn: (data: SaveProfileRequest) => saveImportProfile(data),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: importKeys.profiles })
+    },
+  })
+}
+
+export function useDeleteImportProfile() {
+  const qc = useQueryClient()
+  return useMutation({
+    mutationFn: (id: string) => deleteImportProfile(id),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: importKeys.profiles })
+    },
+  })
+}