test: add unit and integration test suites

- Extract evaluateCondition + rule types into src/lib/rules.ts for testability
- 48 unit tests for evaluateCondition (all fields/operators) and formatCategory
- 21 integration tests for getTransactions filters and getParticipantBalances
- Vitest configs for unit (vitest.config.ts) and integration (vitest.integration.config.ts)
- setup-test-db.sh creates personal_test DB from production schema via pg_dump
- Use vi.doMock + dynamic import pattern to isolate test DB from Prisma singleton

src/__tests__/integration/helpers.ts

@@ -0,0 +1,83 @@
+import { Pool } from "pg";
+import { vi } from "vitest";
+
+export function createPool() {
+  return new Pool({ connectionString: process.env.DATABASE_URL });
+}
+
+// Replace the app's Prisma-based queryRaw with a direct pg call so that
+// tests don't depend on Prisma's singleton picking up the right DATABASE_URL.
+// Must be called BEFORE dynamically importing any module that uses @/lib/db.
+// Uses vi.doMock (not vi.mock) so it is NOT hoisted and CAN close over `p`.
+export function mockDbWithPool(p: Pool) {
+  vi.resetModules(); // clear module cache so fresh imports pick up the mock
+  vi.doMock("@/lib/db", () => ({
+    queryRaw: async (sql: string, params: unknown[] = []) => {
+      const result = await p.query(sql, params);
+      return result.rows;
+    },
+    prisma: p,
+  }));
+}
+
+/** Wipe all data tables and restart sequences between tests. */
+export async function resetDB(pool: Pool) {
+  await pool.query(`
+    TRUNCATE
+      split_payments,
+      transaction_splits,
+      transaction_tags,
+      transaction_overrides,
+      rule_apply_runs,
+      rules,
+      budgets,
+      account_owner_mappings,
+      transactions,
+      statements,
+      tags,
+      participants
+    RESTART IDENTITY CASCADE
+  `);
+}
+
+/** Seed two participants and return their IDs. */
+export async function seedParticipants(pool: Pool, names: [string, string] = ["Alice", "Bob"]) {
+  const r1 = await pool.query(
+    `INSERT INTO participants (name) VALUES ($1) RETURNING id`,
+    [names[0]]
+  );
+  const r2 = await pool.query(
+    `INSERT INTO participants (name) VALUES ($1) RETURNING id`,
+    [names[1]]
+  );
+  return { ownerId: r1.rows[0].id as number, otherId: r2.rows[0].id as number };
+}
+
+/** Insert a manual transaction (no statement) and return its id. */
+export async function insertTransaction(
+  pool: Pool,
+  ownerId: number,
+  overrides: {
+    description?: string;
+    amount?: number;
+    category?: string;
+    transaction_type?: string;
+    transaction_date?: string;
+    merchant_normalized?: string;
+  } = {}
+): Promise<number> {
+  const r = await pool.query(
+    `INSERT INTO transactions
+       (owner_id, statement_id, transaction_date, description, amount, transaction_type, category, row_index)
+     VALUES ($1, NULL, $2, $3, $4, $5, $6, 0) RETURNING id`,
+    [
+      ownerId,
+      overrides.transaction_date ?? "2024-06-15",
+      overrides.description ?? "Test transaction",
+      overrides.amount ?? 100,
+      overrides.transaction_type ?? "debit",
+      overrides.category ?? "other",
+    ]
+  );
+  return r.rows[0].id as number;
+}