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)/reports/page.tsx

@@ -1,9 +1,22 @@
 import { Suspense } from "react";
 import { ReportsPageClient } from "@/components/reports/ReportsPageClient";
-import { aggregateEvents, aggregateReport, sumValues, totalForRows, type EventGroupDimension, type GroupDimension, type Measure } from "@/lib/reports";
+import {
+  aggregateEvents,
+  aggregateReport,
+  parseEventDateParam,
+  parseEventGroupDimension,
+  parseEventSplitDimension,
+  parseEventType,
+  parseGroupDimension,
+  parseIsoDateParam,
+  parseMeasure,
+  parseMode,
+  parseSplitDimension,
+  sumValues,
+  totalForRows,
+} from "@/lib/reports";
 import { loadEventHistory, loadOrgLookups, loadSnapshotEmployees } from "@/lib/reports-data";
 import { createClient } from "@/lib/supabase/server";
-import type { HistoryEventType } from "@/lib/supabase/types";
 
 type SearchParams = {
   mode?: string;
@@ -23,7 +36,7 @@ type SearchParams = {
 export default async function ReportsPage({ searchParams }: { searchParams: Promise<SearchParams> }) {
   const params = await searchParams;
   const supabase = await createClient();
-  const mode = params.mode === "events" ? "events" : "snapshot";
+  const mode = parseMode(params.mode);
 
   const [{ lookups, divisions, locations }, { data: userRes }] = await Promise.all([loadOrgLookups(supabase), supabase.auth.getUser()]);
   const user = userRes.user;
@@ -32,12 +45,20 @@ export default async function ReportsPage({ searchParams }: { searchParams: Prom
     : { data: [] };
 
   if (mode === "events") {
-    const group = (params.group as EventGroupDimension) || "event_type";
-    const split = (params.split as EventGroupDimension) || undefined;
-    const eventType = (params.eventType as HistoryEventType) || undefined;
+    const group = parseEventGroupDimension(params.group);
+    const split = parseEventSplitDimension(params.split);
+    const eventType = parseEventType(params.eventType);
+    const from = parseEventDateParam(params.from);
+    const to = parseEventDateParam(params.to);
 
-    const events = await loadEventHistory(supabase, { eventType, division: params.division, location: params.location, from: params.from, to: params.to });
-    const rows = aggregateEvents(events, group, split ?? null, lookups);
+    const events = await loadEventHistory(supabase, {
+      eventType: eventType ?? undefined,
+      division: params.division,
+      location: params.location,
+      from,
+      to,
+    });
+    const rows = aggregateEvents(events, group, split, lookups);
     const total = sumValues(rows);
 
     return (
@@ -47,7 +68,7 @@ export default async function ReportsPage({ searchParams }: { searchParams: Prom
           eventGroup={group}
           eventSplit={split ?? ""}
           eventType={eventType ?? ""}
-          eventFilters={{ division: params.division ?? "", location: params.location ?? "", from: params.from ?? "", to: params.to ?? "" }}
+          eventFilters={{ division: params.division ?? "", location: params.location ?? "", from: from ?? "", to: to ?? "" }}
           rows={rows}
           total={total}
           recordCount={events.length}
@@ -59,10 +80,10 @@ export default async function ReportsPage({ searchParams }: { searchParams: Prom
     );
   }
 
-  const measure = (params.measure as Measure) || "headcount";
-  const group = (params.group as GroupDimension) || "division";
-  const split = (params.split as GroupDimension) || undefined;
-  const asOf = params.asOf || undefined;
+  const measure = parseMeasure(params.measure);
+  const group = parseGroupDimension(params.group);
+  const split = parseSplitDimension(params.split);
+  const asOf = parseIsoDateParam(params.asOf);
 
   const employees = await loadSnapshotEmployees(supabase, {
     division: params.division,
@@ -71,7 +92,7 @@ export default async function ReportsPage({ searchParams }: { searchParams: Prom
     employment: params.employment,
     asOf,
   });
-  const rows = aggregateReport(employees, measure, group, split ?? null, lookups, asOf);
+  const rows = aggregateReport(employees, measure, group, split, lookups, asOf);
   const total = totalForRows(rows, measure);
 
   return (