Task #514: Align note composer with folders rail

Original task: On the Notes page, the "اكتب ملاحظة" composer sat alone
in a full-width row above the content row, while the "المجلدات"
FoldersRail started in the row below it. The result was a visible
vertical mismatch — composer high, rail noticeably lower with empty
space between them.

Change: Moved the top composer out of its standalone full-width block
and into the left content column (`flex-1 min-w-0`) at the top of the
existing row that already hosts the FoldersRail. Both now share the
same row, so the composer's top edge aligns with the rail's top edge.

Details:
- Single edit in `artifacts/tx-os/src/pages/notes.tsx`.
- The composer's `data-testid="notes-top-composer"` is preserved, so
  any existing E2E selectors continue to work.
- `showTopComposer` gating (hide on Inbox/Sent/Archived/Shared-with-me)
  is unchanged — only the position of the rendered block moved.
- Removed the old wrapper's `px-4 pt-1 max-w-6xl w-full mx-auto`
  (those paddings/centering are now provided by the parent row), and
  added a `mb-4` for breathing room between composer and the content
  below it inside the column.
- Responsive behavior preserved: the parent row is
  `flex-col md:flex-row`, so on narrow widths the composer still
  stacks above the folders area cleanly with no horizontal overflow.

Verification: pnpm tsc --noEmit on tx-os passes; no test files
reference the composer block by structural selectors that the move
would break.

No deviations from the plan.

artifacts/tx-os/src/pages/notes.tsx

@@ -773,19 +773,13 @@ export default function NotesPage() {
           the document so iOS Safari collapses the URL bar on scroll.
           The sticky header above keeps the controls pinned. */}
       <div className="flex-1 flex flex-col">
-      {showTopComposer && (
-        <div
-          className="px-4 pt-1 max-w-6xl w-full mx-auto"
-          data-testid="notes-top-composer"
-        >
-          <Composer
-            labels={labels}
-            folderSelection={folderSelection}
-            onSend={(id) => setSendForNoteId(id)}
-          />
-        </div>
-      )}
 
+      {/* Task #514: composer moved INSIDE the main content column so it
+          shares the same row (and same top edge) as the FoldersRail.
+          Previously it was a standalone full-width block above this
+          row, which made the rail visibly start lower than the
+          composer. Hidden conditions (Inbox/Sent/Archived/Shared) are
+          unchanged — see `showTopComposer`. */}
       <div className="flex-1 px-4 py-6 max-w-6xl w-full mx-auto flex flex-col md:flex-row gap-6">
         {showFolders && (
           <FoldersRail
@@ -799,6 +793,15 @@ export default function NotesPage() {
           />
         )}
         <div className="flex-1 min-w-0">
+        {showTopComposer && (
+          <div className="mb-4" data-testid="notes-top-composer">
+            <Composer
+              labels={labels}
+              folderSelection={folderSelection}
+              onSend={(id) => setSendForNoteId(id)}
+            />
+          </div>
+        )}
         {view === "active" && folderSelection.kind === "shared-folder" && (
           // Recipient view of a folder shared with the current user. Rendered
           // before the regular active branch so we never mount the Composer