feat(trips): trip tracking with analytics, tag conversion, and transaction assignment

Adds trips table usage across API and UI: trip CRUD, per-trip analytics
(category/daily/merchant/tag/participant breakdowns), tag-to-trip
conversion, trip assignment via transaction overrides, and trip filter
in the transactions view. Recovered from working tree after local git
corruption; feature was already live via host-context Docker builds.

src/app/api/trips/[id]/route.ts

@@ -0,0 +1,30 @@
+import { NextRequest, NextResponse } from "next/server";
+import { getCurrentUser } from "@/lib/auth";
+import { getTripById, updateTrip, deleteTrip } from "@/lib/queries";
+
+export async function GET(req: NextRequest, { params }: { params: Promise<{ id: string }> }) {
+  const user = await getCurrentUser(req);
+  if (!user) return NextResponse.json({ error: "Forbidden" }, { status: 403 });
+  const { id } = await params;
+  const trip = await getTripById(Number(id), user.id);
+  if (!trip) return NextResponse.json({ error: "Not found" }, { status: 404 });
+  return NextResponse.json(trip);
+}
+
+export async function PATCH(req: NextRequest, { params }: { params: Promise<{ id: string }> }) {
+  const user = await getCurrentUser(req);
+  if (!user) return NextResponse.json({ error: "Forbidden" }, { status: 403 });
+  const { id } = await params;
+  const body = await req.json();
+  const trip = await updateTrip(Number(id), user.id, body);
+  if (!trip) return NextResponse.json({ error: "Not found" }, { status: 404 });
+  return NextResponse.json(trip);
+}
+
+export async function DELETE(req: NextRequest, { params }: { params: Promise<{ id: string }> }) {
+  const user = await getCurrentUser(req);
+  if (!user) return NextResponse.json({ error: "Forbidden" }, { status: 403 });
+  const { id } = await params;
+  await deleteTrip(Number(id), user.id);
+  return new NextResponse(null, { status: 204 });
+}