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`).

supabase/migrations/20260714120300_reorg_undo_append_only.sql

@@ -0,0 +1,59 @@
+-- Make reorg undo respect employee_history's append-only contract
+-- (spec §6.1: "append-only, keine normale
+-- Update-/Delete-Funktion").
+--
+-- The previous undo_reorg deleted the employee_history rows a reorg had
+-- created (functions.sql:549), which required a narrow RLS carve-out
+-- (functions_3.sql's "history_delete_admin_reorg_undo" policy) allowing
+-- hr_admin to delete reorg-tagged history rows. That is the one place in
+-- the whole schema where history was not actually immutable. Fixed by
+-- appending a compensating "Reorganisation rückgängig" history entry per
+-- affected employee instead of deleting anything — the original
+-- Reorganisation rows stay in the record, exactly like every other history
+-- event type. The now-unused delete policy is dropped.
+
+drop policy if exists "history_delete_admin_reorg_undo" on employee_history;
+
+create or replace function undo_reorg(payload jsonb)
+returns void language plpgsql as $$
+declare
+  v_scenario record;
+  v_key text;
+  v_val jsonb;
+  v_name text;
+  v_count int := 0;
+begin
+  perform require_hr_admin();
+  select * into v_scenario from reorg_scenarios where id = (payload->>'scenario_id')::uuid and applied = true;
+  if not found or v_scenario.undo_snapshot is null then
+    raise exception 'Reorganisation kann nicht rückgängig gemacht werden (kein Snapshot vorhanden).';
+  end if;
+
+  -- Any pending (not-yet-applied) deferred moves belonging to this scenario
+  -- are cancelled rather than left to fire later against a since-reverted
+  -- state.
+  update pending_org_changes set status = 'cancelled'
+    where reorg_scenario_id = v_scenario.id and status = 'pending';
+
+  for v_key, v_val in select * from jsonb_each(v_scenario.undo_snapshot)
+  loop
+    update employees set
+      team_id = nullif(v_val->>'team_id','')::uuid,
+      division_id = (v_val->>'division_id')::uuid,
+      manager_id = nullif(v_val->>'manager_id','')::uuid
+    where id = v_key::uuid;
+
+    select first_name || ' ' || last_name into v_name from employees where id = v_key::uuid;
+    insert into employee_history (employee_id, event_date, event_type, description, reorg_scenario_id)
+      values (v_key::uuid, current_date, 'Reorganisation',
+        'Reorganisation "' || v_scenario.name || '" rückgängig gemacht — vorheriges Team wiederhergestellt', v_scenario.id);
+
+    v_count := v_count + 1;
+  end loop;
+
+  update reorg_scenarios set applied = false where id = v_scenario.id;
+
+  insert into audit_log (actor_user_id, actor_name, action, target_label, details)
+    values (auth.uid(), current_actor_name(), 'Reorganisation rückgängig', v_scenario.name, v_count || ' Mitarbeiter:innen zurückgesetzt');
+end;
+$$;