M0: foundation — monorepo, PostGIS schema, deck query, app shell

Greenfield scaffold for Linkder, a swipe-to-hire marketplace for local
professional services.

- pnpm/turbo monorepo: apps/web, packages/{shared,db}
- Postgres 16 + PostGIS via docker compose (ports 5442/6389 to avoid
  clashing with other local stacks)
- Drizzle schema, 23 tables, geography(Point,4326) with GiST indexes
- Domain core in packages/shared: integer-cent money, status transition
  graphs, deck ranking weights, cancellation policy — 46 unit tests
- Deck query: filtering in Postgres on the GiST index, ranking in JS so
  the weights stay tunable — 18 integration tests against a seeded DB
- Deterministic seed placing pros at known distances, including three
  that must NOT appear on a deck (out of radius, unverified, away)
- Next.js 15 app shell with a working swipe deck
- CI: typecheck, lint, test, build against live postgres+redis

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/shared/src/money.ts

@@ -0,0 +1,51 @@
+/**
+ * Money is always integer minor units (cents). Never floats — 0.1 + 0.2 problems
+ * become customer support tickets when they happen to someone's payout.
+ */
+
+export type Cents = number;
+
+export class MoneyError extends Error {}
+
+export function assertCents(value: number, label = 'amount'): asserts value is Cents {
+  if (!Number.isInteger(value)) throw new MoneyError(`${label} must be an integer, got ${value}`);
+  if (value < 0) throw new MoneyError(`${label} must not be negative, got ${value}`);
+  if (!Number.isSafeInteger(value)) throw new MoneyError(`${label} exceeds safe integer range`);
+}
+
+/** Basis points: 1500 bps = 15%. */
+export type Bps = number;
+
+/**
+ * Platform commission. Rounds half-up so the platform never takes a fraction of a
+ * cent more than stated, and the pro's share absorbs the remainder.
+ */
+export function platformFee(amount: Cents, feeBps: Bps): Cents {
+  assertCents(amount);
+  if (!Number.isInteger(feeBps) || feeBps < 0 || feeBps > 10_000) {
+    throw new MoneyError(`feeBps must be an integer in [0, 10000], got ${feeBps}`);
+  }
+  return Math.round((amount * feeBps) / 10_000);
+}
+
+/** What actually lands in the pro's connected account. */
+export function proPayout(amount: Cents, feeBps: Bps): Cents {
+  return amount - platformFee(amount, feeBps);
+}
+
+/** Split a charge into its parts. The two always sum back to `amount`. */
+export function splitCharge(amount: Cents, feeBps: Bps): { fee: Cents; payout: Cents } {
+  const fee = platformFee(amount, feeBps);
+  return { fee, payout: amount - fee };
+}
+
+export function formatCents(amount: Cents, currency = 'EUR', locale = 'en-IE'): string {
+  return new Intl.NumberFormat(locale, { style: 'currency', currency }).format(amount / 100);
+}
+
+export function parseAmountToCents(input: string): Cents {
+  const normalised = input.replace(/[^0-9.,-]/g, '').replace(',', '.');
+  const parsed = Number.parseFloat(normalised);
+  if (Number.isNaN(parsed)) throw new MoneyError(`Cannot parse "${input}" as an amount`);
+  return Math.round(parsed * 100);
+}