fix(participants): show Me contextually per logged-in user

Participant id=1 was named "Me" in the DB, causing Sonu and other users
to see "Me" referring to Siddharth when viewing splits and shared expenses.

- Rename participant id=1 from "Me" to "Siddharth" in the DB
- /api/participants now substitutes "Me" for whichever participant matches
  the current user, so the label is always relative to the viewer
- split-modal: default split uses currentUser.id instead of name === "Me"
- transactions/page: filter and display logic uses participant ID not name
- shared/page: split chips show "Me" when participant_id === current user

Also includes add-transaction-modal tags support (pre-existing staged change).

src/app/shared/page.tsx

@@ -13,6 +13,7 @@ import {
   type SplitPayment,
 } from "@/lib/hooks";
 import type { SharedTransactionRow } from "@/lib/queries";
+import { EditTransactionModal } from "@/components/edit-transaction-modal";
 
 function formatDate(d: string) {
   return new Date(d).toLocaleDateString("en-AU", { day: "numeric", month: "short", year: "numeric" });
@@ -264,6 +265,7 @@ export default function SharedPage() {
   const [addingParticipant, setAddingParticipant] = useState(false);
   const [paymentModal, setPaymentModal] = useState<{ id: number; name: string; balance: number } | null>(null);
   const [showHistory, setShowHistory] = useState<number | null>(null);
+  const [editModal, setEditModal] = useState<SharedTransactionRow | null>(null);
 
   return (
     <div className="space-y-6">
@@ -352,6 +354,7 @@ export default function SharedPage() {
                 <th className="text-left px-4 py-2 text-xs text-zinc-500 font-medium">Description</th>
                 <th className="text-right px-4 py-2 text-xs text-zinc-500 font-medium">Amount</th>
                 <th className="text-left px-4 py-2 text-xs text-zinc-500 font-medium">Splits</th>
+                <th className="px-4 py-2"></th>
               </tr>
             </thead>
             <tbody>
@@ -377,11 +380,19 @@ export default function SharedPage() {
                         {splits.map((s) => (
                           <span key={s.participant_id}
                             className="inline-flex items-center gap-1 px-2 py-0.5 rounded text-xs bg-zinc-800 text-zinc-300">
-                            {s.name} {s.share_percent}%
+                            {s.participant_id === me?.id ? "Me" : s.name} {s.share_percent}%
                           </span>
                         ))}
                       </div>
                     </td>
+                    <td className="px-4 py-3">
+                      <button
+                        onClick={() => setEditModal(tx)}
+                        className="text-xs text-zinc-500 hover:text-zinc-200 px-2 py-0.5 rounded hover:bg-zinc-800 transition-colors"
+                      >
+                        Edit
+                      </button>
+                    </td>
                   </tr>
                 );
               })}
@@ -399,6 +410,13 @@ export default function SharedPage() {
           onClose={() => setPaymentModal(null)}
         />
       )}
+
+      {editModal && (
+        <EditTransactionModal
+          transaction={editModal}
+          onClose={() => setEditModal(null)}
+        />
+      )}
     </div>
   );
 }