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/lib/rules.ts

@@ -0,0 +1,74 @@
+export interface Condition {
+  field:
+    | "merchant_normalized"
+    | "description"
+    | "category"
+    | "bank_name"
+    | "amount"
+    | "transaction_type"
+    | "tag";
+  operator: "contains" | "equals" | "starts_with" | "gt" | "lt" | "not_equals";
+  value: string;
+}
+
+export interface SplitEntry {
+  participant_id: number;
+  share_percent: number;
+}
+
+export interface Actions {
+  set_category?: string;
+  add_tag_ids?: number[];
+  set_merchant?: string;
+  apply_split?: SplitEntry[];
+}
+
+export interface TxFields {
+  effective_category: string;
+  effective_merchant: string;
+  description: string;
+  bank_name: string;
+  amount: number;
+  transaction_type: string;
+  tags: { id: number }[];
+}
+
+export function evaluateCondition(cond: Condition, tx: TxFields): boolean {
+  if (cond.field === "amount") {
+    const numVal = Number(tx.amount);
+    const numCond = Number(cond.value);
+    switch (cond.operator) {
+      case "equals": return numVal === numCond;
+      case "not_equals": return numVal !== numCond;
+      case "gt": return numVal > numCond;
+      case "lt": return numVal < numCond;
+      default: return false;
+    }
+  }
+
+  if (cond.field === "tag") {
+    const tagId = Number(cond.value);
+    const hasTag = tx.tags.some((t) => t.id === tagId);
+    return cond.operator === "not_equals" ? !hasTag : hasTag;
+  }
+
+  let fieldVal: string;
+  switch (cond.field) {
+    case "merchant_normalized": fieldVal = tx.effective_merchant || ""; break;
+    case "description":         fieldVal = tx.description || ""; break;
+    case "category":            fieldVal = tx.effective_category || ""; break;
+    case "bank_name":           fieldVal = tx.bank_name || ""; break;
+    case "transaction_type":    fieldVal = tx.transaction_type || ""; break;
+    default: return false;
+  }
+
+  const strVal = fieldVal.toLowerCase();
+  const strCond = cond.value.toLowerCase();
+  switch (cond.operator) {
+    case "contains":    return strVal.includes(strCond);
+    case "equals":      return strVal === strCond;
+    case "starts_with": return strVal.startsWith(strCond);
+    case "not_equals":  return strVal !== strCond;
+    default: return false;
+  }
+}