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/OrgChartNode.tsx

@@ -0,0 +1,122 @@
+"use client";
+
+import { Handle, Position, type Node, type NodeProps } from "@xyflow/react";
+import { Building2, ChevronDown, Plus, UserRound } from "lucide-react";
+import Link from "next/link";
+import { memo } from "react";
+import { Avatar } from "@/components/ui/Avatar";
+import { NODE_DIMENSIONS } from "./graphLayout";
+import type { ChartNode, ChartNodeKind } from "./types";
+
+export type OrgChartNodeData = {
+  chartNode: ChartNode;
+  expanded: boolean;
+  hasChildren: boolean;
+  childCount: number;
+  onToggle: (id: string) => void;
+};
+
+export type OrgChartRFNode = Node<OrgChartNodeData, "orgNode">;
+
+// One accent colour per node kind, carried by a left stripe. It is what makes
+// the four kinds separable at a glance when the chart is zoomed out far
+// enough that the text has stopped being legible.
+const KIND_ACCENT: Record<ChartNodeKind, string> = {
+  person: "bg-brand-500",
+  role: "bg-purple-text",
+  group: "bg-ink-muted",
+  vacancy: "bg-brand-200",
+};
+
+const KIND_SHELL: Record<ChartNodeKind, string> = {
+  person: "border-border bg-white",
+  role: "border-border bg-white",
+  group: "border-border-subtle bg-surface",
+  vacancy: "border-dashed border-brand-200 bg-brand-50",
+};
+
+// React Flow re-renders node components on every pan/zoom frame — memo is
+// required, not just tidy, to keep that smooth at a few hundred nodes.
+export const OrgChartNode = memo(function OrgChartNode({ id, data }: NodeProps<OrgChartRFNode>) {
+  const { chartNode, expanded, hasChildren, childCount, onToggle } = data;
+  const { kind, label, sublabel, avatar, href, vacant, totalReports } = chartNode;
+  const isMatch = chartNode.matched ?? false;
+  const { width, height } = NODE_DIMENSIONS[kind];
+
+  const content = (
+    <>
+      {kind === "person" && avatar ? (
+        <Avatar firstName={avatar.firstName} lastName={avatar.lastName} size="sm" />
+      ) : kind === "vacancy" ? (
+        <span className="flex h-7 w-7 shrink-0 items-center justify-center rounded-full border border-dashed border-brand-200 text-brand-500">
+          <Plus className="h-3.5 w-3.5" />
+        </span>
+      ) : kind === "role" ? (
+        <span className="flex h-7 w-7 shrink-0 items-center justify-center rounded-full bg-purple-bg text-purple-text">
+          <UserRound className="h-3.5 w-3.5" />
+        </span>
+      ) : (
+        <span className="flex h-6 w-6 shrink-0 items-center justify-center rounded-full bg-white text-ink-muted">
+          <Building2 className="h-3.5 w-3.5" />
+        </span>
+      )}
+
+      <span className="flex min-w-0 flex-1 flex-col">
+        <span title={label} className="truncate text-[13px] font-bold leading-tight text-ink">
+          {label}
+        </span>
+        {sublabel && (
+          <span
+            title={sublabel}
+            className={`truncate text-[11px] leading-tight ${vacant ? "font-semibold text-warning-text" : "text-ink-muted"}`}
+          >
+            {sublabel}
+          </span>
+        )}
+        {totalReports !== undefined && totalReports > 0 && (
+          <span className="mt-0.5 text-[10px] font-semibold uppercase tracking-wide text-ink-muted">
+            {childCount} direkt · {totalReports} gesamt
+          </span>
+        )}
+      </span>
+    </>
+  );
+
+  return (
+    <div
+      style={{ width, height }}
+      className={`group relative flex items-center overflow-visible rounded-lg border shadow-sm transition-shadow hover:shadow-md ${
+        KIND_SHELL[kind]
+      } ${isMatch ? "ring-2 ring-brand-500 ring-offset-1" : ""}`}
+    >
+      <Handle type="target" position={Position.Top} isConnectable={false} className="!invisible" />
+
+      {/* Accent stripe, inset so it follows the card's rounded corner. */}
+      <span className={`absolute inset-y-1.5 left-0 w-1 rounded-r ${KIND_ACCENT[kind]}`} />
+
+      {href ? (
+        <Link href={href} className="nodrag nopan flex min-w-0 flex-1 items-center gap-2.5 py-2 pl-3.5 pr-3">
+          {content}
+        </Link>
+      ) : (
+        <div className="flex min-w-0 flex-1 items-center gap-2.5 py-2 pl-3.5 pr-3">{content}</div>
+      )}
+
+      {/* Overhangs the bottom edge, sitting on the connector to its children —
+          the conventional org-chart affordance, and a 28px touch target. */}
+      {hasChildren && (
+        <button
+          type="button"
+          onClick={() => onToggle(id)}
+          aria-expanded={expanded}
+          aria-label={expanded ? `${label} zuklappen` : `${label} aufklappen (${childCount})`}
+          className="nodrag nopan absolute -bottom-3.5 left-1/2 z-10 flex h-7 min-w-7 -translate-x-1/2 items-center justify-center rounded-full border border-border bg-white px-1.5 text-[11px] font-bold text-ink-body shadow-sm transition-colors hover:border-brand-500 hover:bg-brand-500 hover:text-white"
+        >
+          {expanded ? <ChevronDown className="h-3.5 w-3.5" /> : childCount}
+        </button>
+      )}
+
+      <Handle type="source" position={Position.Bottom} isConnectable={false} className="!invisible" />
+    </div>
+  );
+});