feat: deterministic seed, impersonation migration, test factories (GRO-110)

Phase 1 — Seed Hardening:
- Replace all Math.random() calls in seed.ts with a Mulberry32 seeded PRNG
  (seed 42) so the same data set is reproduced on every run
- Replace crypto.randomUUID() with a PRNG-based UUID v4 generator
- Add manager (Jordan Lee) and receptionist (Sam Rivera) staff members
  to seed — previously all staff were groomers
- New packages/db/src/reset.ts drops all tables/enums and re-runs
  migrate + seed; exposed as `pnpm db:reset` at root
- Generate migration 0010_impersonation_sessions.sql for the
  impersonation_sessions and impersonation_audit_logs tables that were
  already in schema.ts but had no corresponding migration

Phase 2 — Test Factories:
- New packages/db/src/factories.ts with buildStaff, buildClient, buildPet,
  buildService, buildAppointment and resetFactoryCounters helpers
- Exported via @groombook/db/factories subpath (package.json + vitest alias)
- impersonation.test.ts updated to use buildStaff instead of hand-rolled
  fixture objects

Closes #90 (Phases 1 + 2)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/db/src/reset.ts

@@ -0,0 +1,70 @@
+/**
+ * reset.ts — Drop all application tables and re-run migrations + seed.
+ *
+ * Intended for local development only. Never run against production.
+ *
+ * Usage:
+ *   DATABASE_URL=postgres://... npx tsx packages/db/src/reset.ts
+ */
+
+import postgres from "postgres";
+
+async function reset() {
+  const url = process.env.DATABASE_URL;
+  if (!url) {
+    console.error("DATABASE_URL is not set");
+    process.exit(1);
+  }
+
+  if (process.env.NODE_ENV === "production") {
+    console.error("[FATAL] db:reset must not be run in production.");
+    process.exit(1);
+  }
+
+  const client = postgres(url, { max: 1 });
+
+  console.log("Dropping all application tables...\n");
+
+  // Drop in dependency order (children before parents)
+  await client`
+    DO $$ DECLARE
+      r RECORD;
+    BEGIN
+      FOR r IN (
+        SELECT tablename FROM pg_tables
+        WHERE schemaname = 'public'
+      ) LOOP
+        EXECUTE 'DROP TABLE IF EXISTS public.' || quote_ident(r.tablename) || ' CASCADE';
+      END LOOP;
+    END $$;
+  `;
+
+  // Drop custom enums
+  await client`
+    DO $$ DECLARE
+      r RECORD;
+    BEGIN
+      FOR r IN (
+        SELECT typname FROM pg_type
+        WHERE typtype = 'e' AND typnamespace = (
+          SELECT oid FROM pg_namespace WHERE nspname = 'public'
+        )
+      ) LOOP
+        EXECUTE 'DROP TYPE IF EXISTS ' || quote_ident(r.typname) || ' CASCADE';
+      END LOOP;
+    END $$;
+  `;
+
+  // Drop the drizzle migrations tracking table
+  await client`DROP TABLE IF EXISTS drizzle.__drizzle_migrations CASCADE`;
+  await client`DROP SCHEMA IF EXISTS drizzle CASCADE`;
+
+  console.log("✓ All tables and enums dropped\n");
+
+  await client.end();
+}
+
+reset().catch((err) => {
+  console.error("Reset failed:", err);
+  process.exit(1);
+});