test: real backend pytest + E2E Playwright suites, both isolated from prod data

backend/tests/: 33 pytest tests against a real Postgres database
(aurum_test, created/migrated/dropped per run) exercised through the actual
HTTP API — not sqlite, not mocks, and the real `aurum` database is never
opened (app lifespan is skipped, get_session is overridden per test).
Covers transaction category-kind validation, year/month/date-range
filtering and pagination, dashboard summary arithmetic, budget status, cash
flow, and the /transactions/years picker.

e2e/: 6 Playwright specs driving a real browser against a fully separate
throwaway docker-compose stack (run.sh: separate project name, database,
port, and volume, torn down with `down -v` on exit) — regression coverage
for the Recent Transactions month bug, the Card grid-overflow bug, the
frozen-year bug, the Net Worth default range, and the Dashboard->
Transactions deep link, all fixed earlier this session.

Also synced the backend's APP_VERSION constant (stale at 0.15.2, embedded
in exported backups) with the frontend version.

e2e/tests/helpers.ts

@@ -0,0 +1,36 @@
+import type { APIRequestContext } from "@playwright/test";
+
+/** Thin wrapper over the real HTTP API (proxied at /api by nginx, same as
+ * the frontend uses) — fast, reliable fixture setup so each spec can drive
+ * the actual UI against known data instead of guessing at pre-existing
+ * account/category IDs. */
+
+export async function getDefaultAccountId(request: APIRequestContext): Promise<number> {
+  const resp = await request.get("/api/accounts");
+  const accounts = await resp.json();
+  return accounts[0].id;
+}
+
+export async function getCategoryId(request: APIRequestContext, name: string): Promise<number> {
+  const resp = await request.get("/api/categories");
+  const categories = await resp.json();
+  const match = categories.find((c: { name: string }) => c.name === name);
+  if (!match) throw new Error(`category "${name}" not found`);
+  return match.id;
+}
+
+export interface TransactionInput {
+  account_id: number;
+  category_id?: number;
+  type: "income" | "expense" | "transfer";
+  amount: string;
+  description: string;
+  date: string; // YYYY-MM-DD
+}
+
+export async function createTransaction(request: APIRequestContext, input: TransactionInput): Promise<void> {
+  const resp = await request.post("/api/transactions", { data: input });
+  if (!resp.ok()) {
+    throw new Error(`failed to create transaction: ${resp.status()} ${await resp.text()}`);
+  }
+}