fix(export): paginate the archive size estimate and explain scope counts (#1635)

The period branch of estimateArchiveSize ran a single unpaginated
document read with one flat IN() over every posted entry id in the
year: past the PostgREST row cap it silently undercounts, and past a
few hundred entry ids the URL itself blows up. Chunk the id filter
(CHILD_FK_CHUNK) and paginate every read with fetchAllRows, mirroring
what writeDocuments already did (the ZIP content was never affected).

The dialog now says per scope which documents are counted: full
history includes unlinked inbox/receipt documents, a single year only
those linked to posted vouchers. Without that line, a company with
many unlinked receipts reads the count gap as a pagination bug.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

messages/sv.json

@@ -1422,6 +1422,7 @@
     "default_payment_terms_label": "Betalningsvillkor (dagar)",
     "default_account_label": "Standardkonto",
     "default_account_placeholder": "T.ex. 5410",
+    "default_account_clear": "Rensa standardkonto",
     "default_currency_label": "Standardvaluta",
     "notes_label": "Anteckningar",
     "notes_placeholder": "Interna anteckningar om leverantören...",
@@ -7055,6 +7056,8 @@
     "archive_scope_label": "Omfattning",
     "archive_scope_all": "Hela historiken",
     "archive_scope_period": "Ett räkenskapsår",
+    "archive_scope_all_note": "Allt räkenskapsmaterial, även underlag som ännu inte är kopplade till något verifikat (inkorg och okopplade kvitton).",
+    "archive_scope_period_note": "Underlag kopplade till bokförda verifikat i det valda året. Okopplade underlag ingår bara i Hela historiken.",
     "archive_include_docs_label": "Inkludera kvitton och underlag",
     "archive_include_docs_help": "Bilagor till verifikationer (kvitton, fakturor, PDF:er) packas med i ZIP:en. Stäng av för ett mindre arkiv med bara bokföringsdata.",
     "archive_calculating_size": "Beräknar storlek…",