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/components/add-transaction-modal.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { useState } from "react";
-import { useCreateTransaction, useParticipants } from "@/lib/hooks";
+import { useCreateTransaction, useParticipants, useTags } from "@/lib/hooks";
 import { CATEGORIES, formatCategory } from "@/lib/categories";
 
 const TRANSACTION_TYPES = ["debit", "credit", "payment", "refund", "fee", "interest", "transfer"];
@@ -27,6 +27,7 @@ export function AddTransactionModal({
 }) {
   const createTransaction = useCreateTransaction();
   const { data: participants = [] } = useParticipants();
+  const { data: allTags = [] } = useTags();
 
   const [date, setDate] = useState(prefill?.date ?? new Date().toISOString().slice(0, 10));
   const [description, setDescription] = useState(prefill?.description ?? "");
@@ -34,6 +35,7 @@ export function AddTransactionModal({
   const [type, setType] = useState(prefill?.transaction_type ?? "debit");
   const [merchant, setMerchant] = useState(prefill?.merchant_normalized ?? "");
   const [category, setCategory] = useState(prefill?.category ?? "");
+  const [selectedTagIds, setSelectedTagIds] = useState<number[]>([]);
   const [splits, setSplits] = useState<{ participant_id: number; share_percent: number }[]>(
     prefill?.splits ?? []
   );
@@ -51,9 +53,15 @@ export function AddTransactionModal({
     setSplits(splits.filter((_, idx) => idx !== i));
   }
 
+  function toggleTag(id: number) {
+    setSelectedTagIds((prev) =>
+      prev.includes(id) ? prev.filter((x) => x !== id) : [...prev, id]
+    );
+  }
+
   async function handleSubmit(e: React.FormEvent) {
     e.preventDefault();
-    await createTransaction.mutateAsync({
+    const result = await createTransaction.mutateAsync({
       date,
       description,
       amount: parseFloat(amount),
@@ -62,6 +70,17 @@ export function AddTransactionModal({
       category: category || undefined,
       splits: splits.length ? splits : undefined,
     });
+    if (selectedTagIds.length && result?.id) {
+      await Promise.all(
+        selectedTagIds.map((tagId) =>
+          fetch(`/api/transactions/${result.id}/tags`, {
+            method: "POST",
+            headers: { "Content-Type": "application/json" },
+            body: JSON.stringify({ tag_id: tagId }),
+          })
+        )
+      );
+    }
     onClose();
   }
 
@@ -150,6 +169,37 @@ export function AddTransactionModal({
             />
           </div>
 
+          {/* Tags */}
+          {allTags.length > 0 && (
+            <div>
+              <label className="block text-xs text-zinc-500 mb-1">Tags (optional)</label>
+              <div className="flex flex-wrap gap-1.5">
+                {allTags.map((tag) => {
+                  const selected = selectedTagIds.includes(tag.id);
+                  return (
+                    <button
+                      key={tag.id}
+                      type="button"
+                      onClick={() => toggleTag(tag.id)}
+                      className={`inline-flex items-center gap-1.5 px-2 py-0.5 rounded text-xs border transition-colors ${
+                        selected
+                          ? "border-transparent text-white"
+                          : "border-zinc-600 text-zinc-400 hover:border-zinc-500 hover:text-zinc-300"
+                      }`}
+                      style={selected ? { backgroundColor: tag.color + "cc", borderColor: tag.color } : {}}
+                    >
+                      <span
+                        className="w-1.5 h-1.5 rounded-full flex-shrink-0"
+                        style={{ backgroundColor: tag.color }}
+                      />
+                      {tag.name}
+                    </button>
+                  );
+                })}
+              </div>
+            </div>
+          )}
+
           {/* Splits */}
           <div>
             <div className="flex items-center justify-between mb-1">