Org assignment history, mobile support, and a correctness pass

Data model
- employee_assignments records org placement over time (valid_from/valid_to),
  written by a trigger on `employees` rather than inside each RPC: ~70
  `update employees` statements spread over fifteen migrations mean per-call
  bookkeeping would miss paths today and again with every future RPC. A
  partial unique index enforces the one-open-interval invariant the trigger
  relies on when closing the current row.
- The Organigramm gains a Stichtag (default today). Membership comes from
  entry/exit/karenz, past placement from the new history, future placement
  projected from pending_org_changes. Placements predating the migration are
  backfilled with today's values and flagged as such in the UI, since
  employee_history only ever stored free text and cannot be reconstructed.

Correctness
- Reports and exports silently truncated at PostgREST's 1000-row cap
  (db.max_rows); employee_history is already past it at ~800 staff. Every
  whole-table read now pages explicitly.
- XLSX date cells were a day early: ExcelJS converts a Date to an Excel
  serial straight off getTime(), so a Date built at local midnight lands on
  the previous day's serial in any positive-offset zone.
- Date handling is pinned to Europe/Vienna throughout, and date-only strings
  are formatted without a Date round-trip. The dashboard's YTD window was
  built by round-tripping a local Date through toISOString(), which shifted
  it a day early and dropped 31 December entirely.
- Export routes parsed measure/group/split/eventType with unchecked `as`
  casts, so an unknown value reached column headers as `undefined` and the
  Content-Disposition filename. Parsed against the label maps now, with the
  filename slugged as a backstop.
- toXlsx keyed columns by header text, silently dropping the second of any
  two columns sharing a name — split columns take their header from data.
- The org chart tree walks had no cycle guard; nothing in the schema forbids
  a manager_id cycle, and one would hang the tab rather than misreport.
- The login page reflected ?error= verbatim, letting anyone put arbitrary
  text on the real sign-in screen; messages are looked up by code now.
- React Flow needs elementsSelectable on, or it sets pointer-events:none on
  the whole node and the expand control stops responding.

UI
- Mobile: the shell was unusable below lg — a fixed 236px margin pushed
  content off-screen with no mobile navigation at all. The sidebar is now a
  drawer, dvh replaces vh, safe-area insets are honoured, inputs are 16px so
  iOS stops zooming on focus, and form grids stack.
- Org chart nodes redesigned: per-kind accent stripes and icons, vacant
  roles called out, expand control moved to the bottom edge carrying the
  child count.
- Pagination is windowed; it previously rendered one link per page (54 for
  the employee list, unbounded for the audit log).
- Positions page reduced to open positions with a single "Besetzen" action.
- The employee Organisation tab links into the org chart focused on that
  person, reusing the chart's existing search-match highlighting.

Also included, uncommitted until now
- Dependants, HR notes, academic titles, split address fields, position
  validity and role/employment fields, with their migrations and UI.
- Docker/compose deployment setup, data-model and security-review docs.

app/(app)/layout.tsx

@@ -1,8 +1,8 @@
 import { redirect } from "next/navigation";
 import type { ReactNode } from "react";
 import { HireWizardProvider } from "@/components/hire/HireWizardContext";
-import { Sidebar } from "@/components/shell/Sidebar";
-import { Topbar } from "@/components/shell/Topbar";
+import { AppShell } from "@/components/shell/AppShell";
+import { loadOpenNotes } from "@/lib/notes";
 import { loadOpenPositions } from "@/lib/positions";
 import { createClient } from "@/lib/supabase/server";
 
@@ -22,23 +22,18 @@ export default async function AppLayout({ children }: { children: ReactNode }) {
 
   const userLabel = profile.full_name || profile.email || user.email || "";
 
-  const [openPositions, locationsRes, draftsRes] = await Promise.all([
+  const [openPositions, locationsRes, draftsRes, openNotes] = await Promise.all([
     loadOpenPositions(supabase),
     supabase.from("locations").select("id, name, country").order("name"),
     supabase.from("hire_drafts").select("id, step, payload, updated_at").eq("created_by", user.id).order("updated_at", { ascending: false }),
+    loadOpenNotes(supabase),
   ]);
 
   return (
     <HireWizardProvider openPositions={openPositions} locations={locationsRes.data ?? []} drafts={draftsRes.data ?? []}>
-      <div className="flex min-h-screen">
-        <Sidebar />
-        <div className="ml-[236px] flex flex-1 flex-col">
-          <Topbar userLabel={userLabel} />
-          <main className="flex-1 px-6 py-6">
-            <div className="mx-auto w-full max-w-[1280px]">{children}</div>
-          </main>
-        </div>
-      </div>
+      <AppShell userLabel={userLabel} openNotes={openNotes}>
+        {children}
+      </AppShell>
     </HireWizardProvider>
   );
 }