notes: tighten gap above top composer (Task #447)

The composer wrapper that sits directly under the fixed header's
height-matching spacer had `pt-4` (16px) on top, which made an obvious
empty band between the bottom border of the frozen header and the top
of the "اكتب ملاحظة..." card. Reduced that to `pt-1` (4px) so the
composer now sits flush under the bar with a minimal breathing space,
without affecting the rest of the page (folders rail / browser keep
their own `py-6`).

artifacts/tx-os/src/pages/notes.tsx:497 — single class change.

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

@@ -494,7 +494,7 @@ export default function NotesPage() {
 
       {showTopComposer && (
         <div
-          className="px-4 pt-4 max-w-6xl w-full mx-auto"
+          className="px-4 pt-1 max-w-6xl w-full mx-auto"
           data-testid="notes-top-composer"
         >
           <Composer