feat(seed): ~5x richer demo data via deterministic generators

Rewrite scripts/seed-demo.ts as a thin orchestrator over a new scripts/seed/ module (rng, pools, helpers, content, schedule, logs, generators). Scales demo data from 6 users/3 projects to ~30 users/15 projects with ~5-8x per-table content (~6.8x total rows) via a seeded mulberry32 PRNG for full reproducibility (incl. bcrypt salts and file/URL identifiers). FK-safe ordering, real captured IDs for activity logs, enum pools typed against lib/types. Preserves canonical login credentials and projects.

scripts/seed/rng.ts

@@ -0,0 +1,50 @@
+/**
+ * シードデータ生成用の決定論的乱数ユーティリティ。
+ * mulberry32 を用い、固定シードで再現可能なデータを生成する。
+ */
+
+export type Rng = () => number;
+
+export function createRng(seed: number): Rng {
+  let a = seed >>> 0;
+  return () => {
+    a |= 0;
+    a = (a + 0x6d2b79f5) | 0;
+    let t = Math.imul(a ^ (a >>> 15), 1 | a);
+    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
+    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
+  };
+}
+
+export function pick<T>(rng: Rng, arr: readonly T[]): T {
+  return arr[Math.floor(rng() * arr.length)]!;
+}
+
+export function pickN<T>(rng: Rng, arr: readonly T[], n: number): T[] {
+  return shuffle(rng, arr).slice(0, Math.min(n, arr.length));
+}
+
+export function randInt(rng: Rng, min: number, max: number): number {
+  return Math.floor(rng() * (max - min + 1)) + min;
+}
+
+export function shuffle<T>(rng: Rng, arr: readonly T[]): T[] {
+  const out = [...arr];
+  for (let i = out.length - 1; i > 0; i--) {
+    const j = Math.floor(rng() * (i + 1));
+    [out[i], out[j]] = [out[j]!, out[i]!];
+  }
+  return out;
+}
+
+export function chance(rng: Rng, p: number): boolean {
+  return rng() < p;
+}
+
+export function seededUuid(rng: Rng): string {
+  const hex = () =>
+    Math.floor(rng() * 0x10000)
+      .toString(16)
+      .padStart(4, '0');
+  return `${hex()}${hex()}-${hex()}-${hex()}-${hex()}-${hex()}${hex()}${hex()}`;
+}