feat: initial finance SPA — phases 1 & 2

Next.js 16 personal finance dashboard connected to postgres-personal.

Phase 1 (Foundation):
- API routes: GET /api/transactions (paginated, filterable, sortable),
  GET /api/statements, GET /api/merchants
- Transactions data table with date/category/bank/search filters, pagination, sort
- Statements card grid with period, due date, amount, transaction count
- Sidebar layout with nav for all planned sections

Phase 2 (Normalisation):
- PATCH /api/transactions/[id] — upsert transaction_overrides
- POST /api/transactions/bulk — bulk categorize/normalize
- Inline click-to-edit category (22 options) and merchant name
- Blue dot override indicator, bulk action bar
- Effective values via COALESCE(override, llm_value) pattern

Stack: Next.js 16 (App Router, standalone), Prisma 7.x + @prisma/adapter-pg,
TanStack Query, Tailwind CSS. Auth via Traefik chain-oauth@file.

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

@@ -0,0 +1,46 @@
+import { NextRequest, NextResponse } from "next/server";
+import { getTransactionById } from "@/lib/queries";
+import { prisma } from "@/lib/db";
+
+export async function GET(
+  _req: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  const { id } = await params;
+  const txn = await getTransactionById(Number(id));
+  if (!txn) return NextResponse.json({ error: "Not found" }, { status: 404 });
+  return NextResponse.json(txn);
+}
+
+export async function PATCH(
+  req: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  const { id } = await params;
+  const transactionId = Number(id);
+  const body = await req.json();
+
+  const { category, merchant_normalized, notes } = body as {
+    category?: string;
+    merchant_normalized?: string;
+    notes?: string;
+  };
+
+  const data: Record<string, unknown> = { updated_at: new Date() };
+  if (category !== undefined) data.category_override = category;
+  if (merchant_normalized !== undefined) data.merchant_normalized = merchant_normalized;
+  if (notes !== undefined) data.notes = notes;
+
+  const override = await prisma.transaction_overrides.upsert({
+    where: { transaction_id: transactionId },
+    update: data,
+    create: {
+      transaction_id: transactionId,
+      category_override: category || null,
+      merchant_normalized: merchant_normalized || null,
+      notes: notes || null,
+    },
+  });
+
+  return NextResponse.json(override);
+}