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/lib/api/imports.ts

@@ -0,0 +1,89 @@
+import { z } from "zod"
+import { del, get, post, put, upload } from "./client"
+
+export const sessionCreatedResponseSchema = z.object({
+  session_id: z.string(),
+  columns: z.array(z.string()),
+  sample_rows: z.array(z.array(z.string())),
+})
+export type SessionCreatedResponse = z.infer<typeof sessionCreatedResponseSchema>
+
+export const sessionStateResponseSchema = z.object({
+  session_id: z.string(),
+  columns: z.array(z.string()),
+  has_mappings: z.boolean(),
+  row_count: z.number(),
+})
+export type SessionStateResponse = z.infer<typeof sessionStateResponseSchema>
+
+export const apiFieldMappingSchema = z.object({
+  source_column: z.string(),
+  domain_field: z.string(),
+  rating_scale: z.number().optional(),
+  date_format: z.string().optional(),
+})
+export type ApiFieldMapping = z.infer<typeof apiFieldMappingSchema>
+
+export const applyMappingRequestSchema = z.object({
+  mappings: z.array(apiFieldMappingSchema),
+})
+export type ApplyMappingRequest = z.infer<typeof applyMappingRequestSchema>
+
+export const confirmRequestSchema = z.object({
+  confirmed_indices: z.array(z.number()),
+})
+export type ConfirmRequest = z.infer<typeof confirmRequestSchema>
+
+export const saveProfileRequestSchema = z.object({
+  session_id: z.string(),
+  name: z.string(),
+})
+export type SaveProfileRequest = z.infer<typeof saveProfileRequestSchema>
+
+export function createImportSession(file: File) {
+  return upload<SessionCreatedResponse>("/import/sessions", file)
+}
+
+export function getImportSession(id: string) {
+  return get<SessionStateResponse>(`/import/sessions/${id}`)
+}
+
+export type PreviewRow = {
+  index: number
+  status: string
+  title?: string
+  release_year?: string
+  director?: string
+  rating?: string
+  watched_at?: string
+  comment?: string
+  errors?: string[]
+}
+
+export type PreviewResponse = {
+  rows: PreviewRow[]
+}
+
+export function getImportPreview(id: string) {
+  return get<PreviewResponse>(`/import/sessions/${id}/preview`)
+}
+
+export function applyMapping(sessionId: string, data: ApplyMappingRequest) {
+  return put(`/import/sessions/${sessionId}/mapping`, data)
+}
+
+export function confirmImport(sessionId: string, data: ConfirmRequest) {
+  return post(`/import/sessions/${sessionId}/confirm`, data)
+}
+
+export function getImportProfiles() {
+  return get<unknown[]>("/import/profiles")
+}
+
+export function saveImportProfile(data: SaveProfileRequest) {
+  return post("/import/profiles", data)
+}
+
+export function deleteImportProfile(id: string) {
+  return del(`/import/profiles/${id}`)
+}