fix: wire "Forward as attachment" into Pro's popped-out email tab

The earlier fix (f3b68194) addressed the Pro/embedded composer-hoisting
path (composing FROM the Mail tab, then getting hoisted into a Pro
tab), but missed a second, entirely separate render path: viewing an
email that's already been popped into its own Pro tab
(components/pro/pro-email-tab-body.tsx). That component renders its
own <EmailViewer> with its own self-contained handleForward - it
fetches its own `email` and opens compose tabs directly via
useProTabStore, with no dependency on page.tsx's pendingDraft/
selectedEmail plumbing at all - so it never had onForwardAsAttachment
wired in the first place. The overflow menu there just silently had
no such item, since EmailViewer only renders it when the prop is
provided.

Add handleForwardAsAttachment here, mirroring handleForward but using
the shared buildForwardAsAttachmentPayload helper, with the same
filename-options handling as the page.tsx fix (7a483b3d/a34314ce). No
stale-closure risk here (unlike the list context menu fix) - `email`
is this component's own local per-tab state, not a global selection
being mutated synchronously before the call.

components/pro/pro-email-tab-body.tsx

@@ -15,6 +15,7 @@ import { useProTabStore, type ProEmailTabData, type ProReplyContext } from "@/st
 import type { Email } from "@/lib/jmap/types";
 import { buildReplySubject, buildForwardSubject } from "@/lib/subject-prefix";
 import { getQuoteBodies } from "@/lib/email-composer-utils";
+import { buildForwardAsAttachmentPayload } from "@/lib/forward-as-attachment";
 
 interface ProEmailTabBodyProps {
   tabId: string;
@@ -136,6 +137,44 @@ export function ProEmailTabBody({ tabId, data }: ProEmailTabBodyProps) {
     });
   }, [email, openComposeTab, t]);
 
+  // Mirrors handleForward, but attaches the original as a message/rfc822
+  // file instead of quoting it inline - see lib/forward-as-attachment.ts.
+  // This is a separate, self-contained render path from the main Mail
+  // tab's EmailViewer (page.tsx) - Pro tabs fetch their own `email` and
+  // open compose tabs directly via useProTabStore, not through
+  // page.tsx's pendingDraft/selectedEmail plumbing - so it needed its own
+  // wiring rather than falling out of the page.tsx fix automatically.
+  const handleForwardAsAttachment = useCallback(() => {
+    if (!email) return;
+    const {
+      emailDownloadTemplate,
+      filenameSpaceReplacement,
+      filenameLowercase,
+      filenameStripDiacritics,
+      filenameCollapseSeparators,
+    } = useSettingsStore.getState();
+    const payload = buildForwardAsAttachmentPayload(email, t('email_composer.prefix.forward'), {
+      template: emailDownloadTemplate,
+      spaceReplacement: filenameSpaceReplacement,
+      lowercase: filenameLowercase,
+      stripDiacritics: filenameStripDiacritics,
+      collapseSeparators: filenameCollapseSeparators,
+    });
+    if (!payload) return;
+
+    composerSessionIdRef.current += 1;
+    openComposeTab({
+      sessionId: composerSessionIdRef.current,
+      mode: 'forward',
+      replyTo: {
+        subject: email.subject,
+        attachments: [payload.attachment],
+      },
+      sourceEmailId: email.id,
+      title: payload.subject,
+    });
+  }, [email, openComposeTab, t]);
+
   const handleDelete = useCallback(async () => {
     if (!client || !email) return;
     try {
@@ -283,6 +322,7 @@ export function ProEmailTabBody({ tabId, data }: ProEmailTabBodyProps) {
           onReply={handleReply}
           onReplyAll={handleReplyAll}
           onForward={handleForward}
+          onForwardAsAttachment={handleForwardAsAttachment}
           onDelete={handleDelete}
           onArchive={handleArchive}
           onToggleStar={handleToggleStar}