test(frontend): replay real messages instead of hand-built state literals (WP-70)

Every machine spec redefined its own throwaway fixture helper (editing1/2/3,
editingWith), hardcoding fields like errors: {} that assert against shapes
the reducer may never actually produce. given(reduce, initial)(...msgs)
(libs/shared/src/testing/machine.ts) replaces them by replaying real Msgs
through the real reduce, so a fixture is provably reachable. Adds the same
idiom for value objects (unwrapOk) and RemoteData (loading/success/failure),
plus intake.acceptance.spec.ts as a worked full-journey example.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

libs/shared/src/application/machine-remote-data.spec.ts

@@ -1,9 +1,10 @@
 import { describe, it, expect } from 'vitest';
 import { machineRemoteData } from './machine-remote-data';
+import { loading, success } from '../testing/remote-data';
 
 describe('machineRemoteData', () => {
   it('maps loading → Loading', () => {
-    expect(machineRemoteData({ tag: 'loading' })).toEqual({ tag: 'Loading' });
+    expect(machineRemoteData({ tag: 'loading' })).toEqual(loading());
   });
 
   it('maps failed → Failure carrying an Error with the reason', () => {
@@ -14,6 +15,6 @@ describe('machineRemoteData', () => {
 
   it('maps loaded → Success carrying the whole loaded state', () => {
     const loaded = { tag: 'loaded', foo: 42 } as const;
-    expect(machineRemoteData(loaded)).toEqual({ tag: 'Success', value: loaded });
+    expect(machineRemoteData(loaded)).toEqual(success(loaded));
   });
 });