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>

lib/reports/__tests__/full-archive-export.test.ts

@@ -1037,4 +1037,34 @@ describe('estimateArchiveSize', () => {
     expect(result.document_count).toBe(0)
     expect(result.total_bytes).toBe(8 * 1024 * 1024)
   })
+
+  it('paginates the all-mode document read past the page cap', async () => {
+    const firstPage = Array.from({ length: 1000 }, () => ({ file_size_bytes: 1_000 }))
+    enqueueMany([
+      { data: firstPage }, // full first page forces a second fetch
+      { data: [{ file_size_bytes: 1_000 }] },
+    ])
+
+    const result = await estimateArchiveSize(supabase as any, 'company-1', 'all')
+
+    expect(result.document_count).toBe(1001)
+    expect(result.document_bytes).toBe(1_001_000)
+  })
+
+  it('chunks the period-mode entry-id filter and sums across chunks', async () => {
+    // 250 posted entries -> three IN() chunks of max 100 ids. An unchunked
+    // implementation consumes a single document response and undercounts.
+    const entryIds = Array.from({ length: 250 }, (_, i) => ({ id: `e${i}` }))
+    enqueueMany([
+      { data: entryIds }, // journal_entries for periodEntryIds
+      { data: [{ file_size_bytes: 100 }] }, // chunk 1
+      { data: [{ file_size_bytes: 200 }] }, // chunk 2
+      { data: [{ file_size_bytes: 300 }] }, // chunk 3
+    ])
+
+    const result = await estimateArchiveSize(supabase as any, 'company-1', 'period', 'p-1')
+
+    expect(result.document_count).toBe(3)
+    expect(result.document_bytes).toBe(600)
+  })
 })