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.

components/shell/Topbar.tsx

@@ -1,15 +1,17 @@
 "use client";
 
-import { LogOut } from "lucide-react";
+import { LogOut, Menu } from "lucide-react";
 import { usePathname } from "next/navigation";
 import { logout } from "@/actions/auth";
+import type { OpenNote } from "@/lib/notes";
 import { NewHireButton } from "./NewHireButton";
+import { NotesBell } from "./NotesBell";
 
 const TITLES: Record<string, string> = {
   "/": "Übersicht",
   "/employees": "Mitarbeiter:innen",
   "/orgchart": "Organigramm",
-  "/positions": "Positionen & Bereiche",
+  "/positions": "Positionen",
   "/reports": "Berichte",
   "/audit": "Audit-Log",
 };
@@ -22,20 +24,37 @@ function titleFor(pathname: string): string {
 
 type TopbarProps = {
   userLabel: string;
+  openNotes: OpenNote[];
+  onOpenNav: () => void;
 };
 
-export function Topbar({ userLabel }: TopbarProps) {
+export function Topbar({ userLabel, openNotes, onOpenNav }: TopbarProps) {
   const pathname = usePathname();
 
   return (
-    <header className="flex h-14 items-center justify-between border-b border-border bg-white px-6">
-      <h1 className="text-base font-bold text-ink">{titleFor(pathname)}</h1>
-      <div className="flex items-center gap-4">
+    // Sticky, with the notch inset added to its top padding: on an iPhone in
+    // landscape the bar would otherwise sit under the rounded corner.
+    <header className="sticky top-0 z-20 flex h-14 shrink-0 items-center justify-between border-b border-border bg-white px-3 pt-[env(safe-area-inset-top)] sm:px-6">
+      <div className="flex min-w-0 items-center gap-2">
+        <button
+          type="button"
+          onClick={onOpenNav}
+          aria-label="Navigation öffnen"
+          className="-ml-1 rounded p-2 text-ink-body hover:bg-surface lg:hidden"
+        >
+          <Menu className="h-5 w-5" />
+        </button>
+        <h1 className="truncate text-base font-bold text-ink">{titleFor(pathname)}</h1>
+      </div>
+      <div className="flex shrink-0 items-center gap-1 sm:gap-4">
+        <NotesBell notes={openNotes} />
         <NewHireButton />
-        <div className="flex items-center gap-2 border-l border-border pl-4 text-sm">
-          <span className="font-semibold text-ink">{userLabel}</span>
+        <div className="flex items-center gap-2 text-sm sm:border-l sm:border-border sm:pl-4">
+          {/* The name is the first thing worth dropping on a narrow screen —
+              the account is still reachable via the sign-out control. */}
+          <span className="hidden font-semibold text-ink md:inline">{userLabel}</span>
           <form action={logout}>
-            <button type="submit" aria-label="Abmelden" className="ml-2 rounded p-1.5 text-ink-muted hover:bg-surface">
+            <button type="submit" aria-label="Abmelden" className="rounded p-2 text-ink-muted hover:bg-surface">
               <LogOut className="h-4 w-4" />
             </button>
           </form>