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.

lib/notes.ts

@@ -0,0 +1,26 @@
+import type { SupabaseClient } from "@supabase/supabase-js";
+import { fetchAllRows } from "./supabase/query";
+import type { Database } from "./supabase/types";
+
+export type OpenNote = Database["public"]["Tables"]["employee_notes"]["Row"] & {
+  employeeName: string;
+};
+
+// "Meine Notizen" (Topbar-Glocke): das geteilte, mitarbeiterübergreifende
+// Postfach aller noch nicht erledigten HR-Notizen — unabhängig davon wer
+// sie verfasst hat oder zu wem sie gehören (mit Nutzer abgestimmt). Zwei
+// einfache Queries, in JS gemerged — gleiches Muster wie loadEventHistory
+// in lib/reports-data.ts, da der handgeschriebene Database-Typ keine
+// relationalen Embeddings für eine einzelne verschachtelte Query kennt.
+export async function loadOpenNotes(supabase: SupabaseClient<Database>): Promise<OpenNote[]> {
+  const [{ data: notes }, employees] = await Promise.all([
+    supabase.from("employee_notes").select("*").eq("done", false).order("created_at", { ascending: false }),
+    fetchAllRows(() => supabase.from("employees").select("id, first_name, last_name").order("id")),
+  ]);
+
+  const employeeById = new Map(employees.map((e) => [e.id, e]));
+  return (notes ?? []).map((n) => {
+    const emp = employeeById.get(n.employee_id);
+    return { ...n, employeeName: emp ? `${emp.first_name} ${emp.last_name}` : "Unbekannt" };
+  });
+}