Task #731: details card square corners, attached to booking row, centered cell text

- Expanded booking details in protocol.tsx: TableCell padding p-3 → p-0 so
  the card attaches directly to the booking row with no gap.
- Card container: removed rounded-lg and side border; now border-b
  border-slate-400 only — square corners, flush with table edges.
- Details TableRow gets border-b-0 to avoid a double bottom separator with
  the inner border (architect review fix).
- Grid detail cells (مقدم الطلب، الإدارة، الهاتف...) now text-center for
  both label and value; meeting-name header also centered for consistency.
- UI-only; tsc --noEmit clean.

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

@@ -1218,10 +1218,10 @@ export default function ProtocolPage() {
           </TableCell>
         </TableRow>
         {expanded && (
-          <TableRow key={`${b.id}-details`} className="bg-slate-50/80">
-            <TableCell colSpan={detailColSpan} className="p-3">
-              <div className="overflow-hidden rounded-lg border border-slate-400 bg-white">
-                <div className="border-b border-slate-300 bg-slate-50 px-4 py-2.5">
+          <TableRow key={`${b.id}-details`} className="border-b-0 bg-slate-50/80">
+            <TableCell colSpan={detailColSpan} className="p-0">
+              <div className="overflow-hidden border-b border-slate-400 bg-white">
+                <div className="border-b border-slate-300 bg-slate-50 px-4 py-2.5 text-center">
                   <span className="text-[11px] text-slate-400">
                     {t("protocol.bookings.table.title")}
                   </span>
@@ -1267,7 +1267,7 @@ export default function ProtocolPage() {
                   ).map(([label, value], i) => (
                     <div
                       key={i}
-                      className="border-b border-slate-300 px-4 py-2"
+                      className="border-b border-slate-300 px-4 py-2 text-center"
                     >
                       <div className="text-[11px] text-slate-400">
                         {label}