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`).

components/hire/types.ts

@@ -19,7 +19,6 @@ export type HireDraftData = {
   contractEndDate: string;
   employmentType: EmploymentType;
   weeklyHours: string;
-  salary: string;
   paygrade: PaygradeType;
 };
 
@@ -39,6 +38,5 @@ export const EMPTY_HIRE_DRAFT: HireDraftData = {
   contractEndDate: "",
   employmentType: "Vollzeit",
   weeklyHours: "38.5",
-  salary: "",
   paygrade: "B",
 };