fix(composer): keep From/To/Cc/Bcc/Subject fields pinned above the body

Move the fields section out of the composer's scroll container so it
stays visible while scrolling long bodies, matching the pinned
formatting toolbar. Since the fields were the first child of the
scroll container, hoisting them above it is visually identical to
making them sticky - but needs no dynamic offset for the toolbar's
own sticky top (the fields' height varies with Cc/Bcc toggling and
recipient-chip wrapping). The scroll container now wraps only the
body and the signature preview.

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

components/email/email-composer.tsx

@@ -2598,9 +2598,10 @@ export function EmailComposer({
         )}
       </div>
 
-      <div className="flex-1 min-h-0 overflow-auto">
-        {/* Fields section */}
-        <div className="space-y-0 border-b">
+      {/* Fields section - outside the scroll container so From/To/Cc/Bcc/
+          Subject stay reachable while scrolling long bodies, matching the
+          pinned formatting toolbar (see rich-text-editor.tsx). */}
+      <div className="shrink-0 space-y-0 border-b">
           {/* From field */}
           <div className="flex items-center gap-2 px-4 py-2.5 border-b border-border/50">
             <span className="text-sm text-muted-foreground w-12 md:w-16 shrink-0">{t('from')}:</span>
@@ -2879,8 +2880,9 @@ export function EmailComposer({
               className="flex-1 border-0 focus-visible:ring-0 h-8 px-0 text-sm"
             />
           </div>
-        </div>
+      </div>
 
+      <div className="flex-1 min-h-0 overflow-auto">
         {/* Body */}
         {plainTextMode ? (
           <textarea