fix: give mail import and export their own settings section and name the upload limit as the server does

- Settings > Backup & reset gets a Mail files section for Import mail
  and Export all mail, instead of sitting under settings backup.
- The pause message names Stalwart's 50000000-byte quota as 50 MB, not
  48 MB, and the dialog and settings texts mention .ost files.
- The old import's leftovers go: expandImportableEmails and
  EML_IMPORT_ACCEPT in lib/eml-import.ts, and the strings
  email_viewer.import_email, mailbox_context_menu.import_email and
  notifications.import_email_success/_error in all 30 locales.

lib/__tests__/eml-import.test.ts loses the tests of the removed
functions; its #891 checks that an .eml and an .eml in a ZIP keep their
Date header now run against the import's own sources.

lib/__tests__/eml-import.test.ts

@@ -1,54 +1,18 @@
 import { describe, it, expect } from 'vitest';
-import JSZip from 'jszip';
-import { expandImportableEmails, readMessageDate, EML_IMPORT_ACCEPT } from '@/lib/eml-import';
+import { readMessageDate } from '@/lib/eml-import';
+import { emlSource, zipSource, type ImportItem } from '@/lib/mail-import/sources';
+import { ZipWriter } from '@/lib/mail-export/zip-writer';
 
 const emlFile = (name: string, content = 'raw email', type = 'message/rfc822') =>
   new File([content], name, { type });
 
-describe('expandImportableEmails', () => {
-  it('wraps a .eml file as a message/rfc822 blob, keeping its name', async () => {
-    const out = await expandImportableEmails([emlFile('msg.eml')]);
-    expect(out).toHaveLength(1);
-    expect(out[0].name).toBe('msg.eml');
-    expect(out[0].blob.type).toBe('message/rfc822');
-    await expect(out[0].blob.text()).resolves.toBe('raw email');
-  });
+const opts = { skipBefore: 0, maxMessageBytes: 50_000_000 };
 
-  it('CHARACTERISATION: wraps a non-.eml, non-zip file as rfc822 too', async () => {
-    const out = await expandImportableEmails([emlFile('note.txt', 'hi', 'text/plain')]);
-    expect(out).toHaveLength(1);
-    expect(out[0]).toMatchObject({ name: 'note.txt' });
-    expect(out[0].blob.type).toBe('message/rfc822');
-  });
-
-  it('extracts only .eml entries from a .zip, stripping path prefixes', async () => {
-    const zip = new JSZip();
-    zip.file('a.eml', 'A');
-    zip.file('sub/b.eml', 'B');
-    zip.file('c.txt', 'C'); // skipped (not .eml)
-    zip.folder('emptydir'); // skipped (directory)
-    const blob = await zip.generateAsync({ type: 'blob' });
-    const file = new File([blob], 'archive.zip', { type: 'application/zip' });
-
-    const out = await expandImportableEmails([file]);
-    expect(out.map((e) => e.name).sort()).toEqual(['a.eml', 'b.eml']);
-    expect(out.every((e) => e.blob.type === 'message/rfc822')).toBe(true);
-  });
-
-  it('uses the zip path when the MIME type is application/zip even without a .zip name', async () => {
-    const zip = new JSZip();
-    zip.file('only.eml', 'X');
-    const blob = await zip.generateAsync({ type: 'blob' });
-    const file = new File([blob], 'archive-no-ext', { type: 'application/zip' });
-
-    const out = await expandImportableEmails([file]);
-    expect(out.map((e) => e.name)).toEqual(['only.eml']);
-  });
-
-  it('exposes the accept string for the file picker', () => {
-    expect(EML_IMPORT_ACCEPT).toBe('.eml,.zip,message/rfc822,application/zip');
-  });
-});
+async function all(source: AsyncGenerator<ImportItem>): Promise<ImportItem[]> {
+  const out: ImportItem[] = [];
+  for await (const item of source) out.push(item);
+  return out;
+}
 
 describe('Date header as receivedAt (#891)', () => {
   const CRLF = String.fromCharCode(13, 10);
@@ -63,16 +27,17 @@ describe('Date header as receivedAt (#891)', () => {
   ].join(CRLF);
 
   it('carries the Date header of an .eml file as a JMAP UTCDate', async () => {
-    const out = await expandImportableEmails([emlFile('old.eml', raw)]);
-    expect(out[0].receivedAt).toBe('2019-03-05T08:30:00Z');
+    const [item] = await all(emlSource(emlFile('old.eml', raw), opts));
+    expect(item).toMatchObject({ kind: 'message', receivedAt: '2019-03-05T08:30:00Z' });
   });
 
   it('carries the Date header of each .eml inside a .zip', async () => {
-    const zip = new JSZip();
-    zip.file('old.eml', raw);
-    const blob = await zip.generateAsync({ type: 'blob' });
-    const out = await expandImportableEmails([new File([blob], 'a.zip', { type: 'application/zip' })]);
-    expect(out[0].receivedAt).toBe('2019-03-05T08:30:00Z');
+    const parts: Uint8Array[] = [];
+    const z = new ZipWriter(async (c) => { parts.push(c.slice()); });
+    await z.addFile('old.eml', new TextEncoder().encode(raw));
+    await z.finish();
+    const [item] = await all(zipSource(new File(parts as BlobPart[], 'a.zip', { type: 'application/zip' }), opts));
+    expect(item).toMatchObject({ kind: 'message', receivedAt: '2019-03-05T08:30:00Z' });
   });
 
   it('leaves receivedAt unset when there is no usable Date header', async () => {

lib/eml-import.ts

@@ -1,26 +1,5 @@
 import { MAX_FUTURE_SENT_AT_MS } from "./email-date";
 
-export interface ImportableEmail {
-  name: string;
-  blob: Blob;
-  /**
-   * The message's `Date` header as a JMAP UTCDate, passed as `receivedAt` on
-   * Email/import. Without it the server stamps the import time and every
-   * imported message looks like it arrived today (#891).
-   */
-  receivedAt?: string;
-}
-
-const EMAIL_MIME = "message/rfc822";
-
-function isEmlName(name: string): boolean {
-  return /\.eml$/i.test(name);
-}
-
-function isZipName(name: string): boolean {
-  return /\.zip$/i.test(name);
-}
-
 /** Only the header block is needed; don't decode a whole large message. */
 const HEADER_SCAN_BYTES = 64 * 1024;
 
@@ -46,39 +25,3 @@ export function dateFromHeaderBlock(head: string, now: number = Date.now()): str
   if (Number.isNaN(time) || time - now > MAX_FUTURE_SENT_AT_MS) return undefined;
   return new Date(time).toISOString().replace(/\.\d{3}Z$/, "Z");
 }
-
-async function extractEmlsFromZip(file: File): Promise<ImportableEmail[]> {
-  const { default: JSZip } = await import("jszip");
-  const zip = await JSZip.loadAsync(await file.arrayBuffer());
-  const out: ImportableEmail[] = [];
-  const entries = Object.values(zip.files);
-  for (const entry of entries) {
-    if (entry.dir) continue;
-    if (!isEmlName(entry.name)) continue;
-    const data = await entry.async("arraybuffer");
-    const blob = new Blob([data], { type: EMAIL_MIME });
-    out.push({
-      name: entry.name.split(/[\\/]/).pop() || entry.name,
-      blob,
-      receivedAt: await readMessageDate(blob),
-    });
-  }
-  return out;
-}
-
-export async function expandImportableEmails(
-  files: File[],
-): Promise<ImportableEmail[]> {
-  const out: ImportableEmail[] = [];
-  for (const file of files) {
-    if (isZipName(file.name) || file.type === "application/zip") {
-      out.push(...(await extractEmlsFromZip(file)));
-      continue;
-    }
-    const blob = new Blob([await file.arrayBuffer()], { type: EMAIL_MIME });
-    out.push({ name: file.name, blob, receivedAt: await readMessageDate(blob) });
-  }
-  return out;
-}
-
-export const EML_IMPORT_ACCEPT = ".eml,.zip,message/rfc822,application/zip";