refactor: one member order for the 3 wizard containers (RD-38)

RD-22 and RD-23 brought the wizard containers under the 250-line budget, so
`max-lines` reports nothing. The files still read badly. Line count was never
the problem.

Fix three things in all three containers:

1. The member order was scrambled, and it differed per file. `registratie`
   declared `draftSync` in the middle of a run of `computed`s; `herregistratie`
   read `this.stepLabels.length` seven lines before `stepLabels` existed; the
   three files put the copy arrays in three different places. All three now use
   one nine-section order, so they compare side by side.
2. Pure logic sat in the container. Extract `digitalDocumentIds` into
   `upload.machine.ts` — the "digital and finished uploading" filter was
   written out four times, and it removes a `documentId!` assertion from both
   containers. Extract `diplomaMsg` into a sibling of the step files.
3. Comments carried archaeology. Drop the three RD-05 references and keep the
   rule. Drop "replaces sessionStorage" and the note about focus management that
   moved to the shell. Fix `intake`'s class comment, which claimed answers
   persist to sessionStorage and was contradicted 30 lines below.

`phase` deliberately stays in all three: it cannot live in `domain/`, and three
siblings plus three specs is a worse trade than 17 readable lines. The store ⇄
`draftSync` cycle also stays — both callbacks are deferred, so it is safe, and
one comment now names it.

No behaviour change. Member lists and every `private`/`protected`/`readonly`
modifier are unchanged, which the showcase depends on.

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

apps/ssp/src/app/registratie/domain/registratie-wizard.machine.ts

@@ -9,6 +9,7 @@ import {
   reduceUpload,
   requiredCategoriesSatisfied,
   deliveryRefs,
+  digitalDocumentIds,
 } from '@shared/domain/upload.machine';
 
 /**
@@ -109,7 +110,7 @@ export function hasProgress(s: Extract<RegistratieState, { tag: 'Invullen' }>):
     !!d.email ||
     !!d.diplomaId ||
     !!d.beroep ||
-    deliveryRefs(s.upload).some((r) => r.channel === 'digital' && !!r.documentId)
+    digitalDocumentIds(s.upload).length > 0
   );
 }