fix(GRO-2139): serialize reset→migrate→seed under the seed advisory lock (#160)

Serialize the entire db:reset chain (DROP → migrate → seed) inside one withSeedAdvisoryLock callback so a concurrent same-PRNG seeder cannot interleave and collide on invoices_pkey. Pool sized max:6 (1 reserved for the lock + work headroom) to avoid the connection-starvation deadlock the CTO caught. Verified with three end-to-end live db:reset runs against a throwaway Postgres.

cc @cpfarhood

packages/db/src/seed.ts

@@ -24,9 +24,9 @@ import type { MedicalAlert } from "@groombook/types";
 
 // ── Seed profile configuration ─────────────────────────────────────────────
 
-type SeedProfile = "dev" | "uat" | "demo";
+export type SeedProfile = "dev" | "uat" | "demo";
 
-interface ProfileConfig {
+export interface ProfileConfig {
   staffCount: { manager: number; receptionist: number; groomer: number; bather: number };
   clientCount: number;
   appointmentsBackDays: number;
@@ -35,7 +35,7 @@ interface ProfileConfig {
   includeUatClients: boolean;
 }
 
-const profiles: Record<SeedProfile, ProfileConfig> = {
+export const profiles: Record<SeedProfile, ProfileConfig> = {
   dev: {
     staffCount: { manager: 1, receptionist: 1, groomer: 2, bather: 0 },
     clientCount: 100,
@@ -70,6 +70,8 @@ function getProfile(): SeedProfile {
   return "uat";
 }
 
+export { getProfile };
+
 // ── Deterministic PRNG (Mulberry32) ──────────────────────────────────────────
 
 /**
@@ -1194,7 +1196,7 @@ async function seedKnownUsers() {
 // from runbooks without ambiguity and binds to the single-argument
 // `pg_advisory_lock(int)` form, which postgres-js serializes as a plain
 // number (no bigint type plumbing required).
-const SEED_ADVISORY_LOCK_KEY = 0x47524f4f; // "GROO" in ASCII — arbitrary, stable
+export const SEED_ADVISORY_LOCK_KEY = 0x47524f4f; // "GROO" in ASCII — arbitrary, stable
 
 /**
  * Reserve a dedicated connection from `pool`, take the seed advisory lock
@@ -1207,7 +1209,7 @@ const SEED_ADVISORY_LOCK_KEY = 0x47524f4f; // "GROO" in ASCII — arbitrary, sta
  * for the lock and release it from the same reserved connection. The
  * seed work itself still runs on the pooled connections.
  */
-async function withSeedAdvisoryLock<T>(
+export async function withSeedAdvisoryLock<T>(
   pool: ReturnType<typeof postgres>,
   fn: () => Promise<T>,
 ): Promise<T> {
@@ -1265,7 +1267,7 @@ async function seed() {
   await client.end();
 }
 
-async function runSeedBody(
+export async function runSeedBody(
   client: ReturnType<typeof postgres>,
   db: ReturnType<typeof drizzle>,
   profile: SeedProfile,