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.

backend/tests/test_budgets.py

@@ -0,0 +1,82 @@
+"""Budgets: category-kind restriction, one-budget-per-category, and the
+spent/remaining/over-budget math behind the Budget page's progress bars.
+"""
+from decimal import Decimal
+
+from httpx import AsyncClient
+
+from tests.helpers import money, txn_payload
+
+
+async def test_budget_rejects_income_category(client: AsyncClient, categories):
+    resp = await client.post(
+        "/budgets", json={"category_id": categories["Salary"]["id"], "monthly_limit": "500.00"}
+    )
+    assert resp.status_code == 400
+
+
+async def test_budget_rejects_duplicate_category(client: AsyncClient, categories):
+    category_id = categories["Groceries"]["id"]
+    first = await client.post("/budgets", json={"category_id": category_id, "monthly_limit": "300.00"})
+    assert first.status_code == 201
+
+    second = await client.post("/budgets", json={"category_id": category_id, "monthly_limit": "400.00"})
+    assert second.status_code == 400
+
+
+async def test_status_reports_spent_remaining_and_over_budget(client: AsyncClient, account_id, categories):
+    category_id = categories["Groceries"]["id"]
+    await client.post("/budgets", json={"category_id": category_id, "monthly_limit": "100.00"})
+
+    for amount in ["60.00", "60.00"]:  # 120.00 total, over a 100.00 limit
+        await client.post(
+            "/transactions",
+            json=txn_payload(account_id, amount=amount, category_id=category_id, date="2026-08-10"),
+        )
+
+    resp = await client.get("/budgets/status", params={"year": 2026, "month": 8})
+    item = resp.json()["items"][0]
+    assert money(item["spent"]) == Decimal("120.00")
+    assert money(item["remaining"]) == Decimal("-20.00")
+    assert item["percent"] == 120.0
+    assert item["is_over_budget"] is True
+
+
+async def test_status_only_counts_the_selected_month(client: AsyncClient, account_id, categories):
+    category_id = categories["Groceries"]["id"]
+    await client.post("/budgets", json={"category_id": category_id, "monthly_limit": "100.00"})
+    await client.post(
+        "/transactions", json=txn_payload(account_id, amount="90.00", category_id=category_id, date="2026-07-15")
+    )
+
+    resp = await client.get("/budgets/status", params={"year": 2026, "month": 8})
+    item = resp.json()["items"][0]
+    assert money(item["spent"]) == 0
+    assert item["is_over_budget"] is False
+
+
+async def test_status_is_empty_list_when_no_budgets_exist(client: AsyncClient):
+    resp = await client.get("/budgets/status", params={"year": 2026, "month": 8})
+    assert resp.json()["items"] == []
+
+
+async def test_update_budget_changes_the_limit(client: AsyncClient, categories):
+    category_id = categories["Groceries"]["id"]
+    created = await client.post("/budgets", json={"category_id": category_id, "monthly_limit": "100.00"})
+    budget_id = created.json()["id"]
+
+    resp = await client.patch(f"/budgets/{budget_id}", json={"monthly_limit": "250.00"})
+    assert resp.status_code == 200
+    assert money(resp.json()["monthly_limit"]) == Decimal("250.00")
+
+
+async def test_delete_budget_removes_it_from_status(client: AsyncClient, account_id, categories):
+    category_id = categories["Groceries"]["id"]
+    created = await client.post("/budgets", json={"category_id": category_id, "monthly_limit": "100.00"})
+    budget_id = created.json()["id"]
+
+    delete_resp = await client.delete(f"/budgets/{budget_id}")
+    assert delete_resp.status_code == 204
+
+    status = await client.get("/budgets/status", params={"year": 2026, "month": 8})
+    assert status.json()["items"] == []