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/orgchart/OrgChartClient.tsx

@@ -3,6 +3,7 @@
 import { useState } from "react";
 import { SegmentedControl } from "@/components/ui/SegmentedControl";
 import type { OpenPositionResolved } from "@/lib/positions";
+import { AsOfPicker } from "./AsOfPicker";
 import { EmployeeTree } from "./EmployeeTree";
 import { PositionTree } from "./PositionTree";
 import { ReorgWorkbench } from "./ReorgWorkbench";
@@ -17,10 +18,29 @@ type OrgChartClientProps = {
   teams: OrgTeam[];
   openPositions: OpenPositionResolved[];
   reorgScenarios: ReorgScenarioSummary[];
+  asOf: string;
+  today: string;
+  projectedCount: number;
+  historyStartsAt: string | null;
+  /** Arrived via "Im Organigramm anzeigen" — unfold and centre this person. */
+  focusId: string | null;
 };
 
-export function OrgChartClient({ employees, divisions, departments, teams, openPositions, reorgScenarios }: OrgChartClientProps) {
+export function OrgChartClient({
+  employees,
+  divisions,
+  departments,
+  teams,
+  openPositions,
+  reorgScenarios,
+  asOf,
+  today,
+  projectedCount,
+  historyStartsAt,
+  focusId,
+}: OrgChartClientProps) {
   const [view, setView] = useState<View>("ma");
+  const isToday = asOf === today;
 
   return (
     <div className="flex flex-col gap-4">
@@ -33,13 +53,31 @@ export function OrgChartClient({ employees, divisions, departments, teams, openP
           { value: "reo", label: "Reorganisation" },
         ]}
       />
-      {view === "ma" && <EmployeeTree employees={employees} />}
+
+      {view !== "reo" && (
+        <AsOfPicker asOf={asOf} today={today} projectedCount={projectedCount} historyStartsAt={historyStartsAt} />
+      )}
+
+      {view === "ma" && <EmployeeTree employees={employees} focusId={focusId} />}
       {view === "pos" && (
         <PositionTree employees={employees} divisions={divisions} departments={departments} teams={teams} openPositions={openPositions} />
       )}
-      {view === "reo" && (
-        <ReorgWorkbench employees={employees} divisions={divisions} departments={departments} teams={teams} reorgScenarios={reorgScenarios} />
-      )}
+      {view === "reo" &&
+        (isToday ? (
+          <ReorgWorkbench employees={employees} divisions={divisions} departments={departments} teams={teams} reorgScenarios={reorgScenarios} />
+        ) : (
+          // A reorg planned against a past or projected roster would be
+          // applied to the *live* org anyway — better to send the user back
+          // to today than to let them assemble moves from a roster that is
+          // not the one the change would hit.
+          <div className="rounded border border-border bg-white p-6 text-sm text-ink-body">
+            <p className="font-semibold text-ink">Reorganisation nur zum heutigen Stand</p>
+            <p className="mt-1 text-ink-muted">
+              Es ist ein abweichender Stichtag gewählt. Reorganisationen wirken immer auf die aktuelle Struktur — wechseln
+              Sie zurück auf „Heute“, um eine zu planen.
+            </p>
+          </div>
+        ))}
     </div>
   );
 }