Consolidation pass: HR-only access, effective-dated mutations, data integrity guards, test suite

Reworks the app from a two-role (hr_admin/manager) model to a single
HR-only role gated by profiles.is_active, fixes transfer/promote/karenz/
reorg RPCs to actually defer future-dated changes via a new
pending_org_changes table instead of writing them immediately (applied
by a daily Vercel Cron route), makes reorg undo append-only instead of
deleting history, adds Karenz-return and history-date integrity guards,
deprecates the salary column, and adds explicit schema grants + perf
indexes needed to run against a fresh (non-hosted) Postgres instance.

Adds vitest unit + integration test suites (the latter against a real
local Supabase instance) covering all of the above, plus lint/typecheck/
build wiring (`npm run check`).

app/(app)/audit/page.tsx

@@ -2,7 +2,6 @@ import Link from "next/link";
 import { Suspense } from "react";
 import { AuditFilters } from "@/components/audit/AuditFilters";
 import { actionBadgeStyle } from "@/lib/colors";
-import { fmtDate } from "@/lib/format";
 import { createClient } from "@/lib/supabase/server";
 
 const PAGE_SIZE = 25;