fix(security+trips): auth/ownership on all API routes; trip analytics in AUD

Ten routes accepted requests with no getCurrentUser check (transactions/[id],
bulk, splits, tags-on-tx, splits/settle, statements/[id], tags, tags/[id],
merchants, participants/[id]/balance), and by-id routes did no ownership
check at all — any participant could read or modify another's data.

Adds canAccessTransactions() (owner via statement/direct, or split
participant), applies it to every transaction-scoped route, owner-scopes
statements/[id], and rescopes splits/settle in raw SQL so settlement only
touches splits the caller is party to.

Also: all trip analytics now sum COALESCE(amount_aud, amount) instead of raw
amount, matching every other analytics query — trip totals previously added
foreign-currency amounts to AUD ones unit-less.

And rules apply_split no longer delete+reinserts splits (which reset settled
flags on every run) — it upserts share_percent and removes only participants
no longer in the rule.

src/app/api/transactions/bulk/route.ts

@@ -1,8 +1,11 @@
 import { NextRequest, NextResponse } from "next/server";
 import { prisma, queryRaw } from "@/lib/db";
-import { assignTransactionsToTrip } from "@/lib/queries";
+import { assignTransactionsToTrip, canAccessTransactions } from "@/lib/queries";
+import { getCurrentUser } from "@/lib/auth";
 
 export async function POST(req: NextRequest) {
+  const user = await getCurrentUser(req);
+  if (!user) return NextResponse.json({ error: "Unauthorized" }, { status: 403 });
   const body = await req.json();
   const { action, ids, category, merchant_normalized, splits, tag_id } = body as {
     action: string;
@@ -17,6 +20,10 @@ export async function POST(req: NextRequest) {
     return NextResponse.json({ error: "ids required" }, { status: 400 });
   }
 
+  if (!(await canAccessTransactions(user.id, ids.map(Number)))) {
+    return NextResponse.json({ error: "Not found" }, { status: 404 });
+  }
+
   if (action === "categorize" && category) {
     const ops = ids.map((id) =>
       prisma.transaction_overrides.upsert({