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/globals.css

@@ -42,4 +42,96 @@
 body {
   background-color: var(--color-surface);
   color: var(--color-ink);
+  /* iOS bounce-scrolls the whole document behind fixed overlays (drawer,
+     modal) and shows the white page edge; contain keeps the rubber band
+     inside the scroller that actually overflowed. */
+  overscroll-behavior-y: none;
+}
+
+/* Mobile browsers zoom the page when a focused input is under ~16px. Every
+   form control in this app is text-sm (14px), so without this, tapping any
+   field on iOS Safari jumps the layout. */
+@media (max-width: 767px) {
+  input,
+  select,
+  textarea {
+    font-size: 16px;
+  }
+}
+
+/* Touch devices have no hover, so the grey flash Chrome/Safari paint on tap
+   is the only press feedback — but their default is a hard blue box. */
+@media (hover: none) {
+  * {
+    -webkit-tap-highlight-color: color-mix(in srgb, var(--color-brand-500) 12%, transparent);
+  }
+}
+
+/* ── React Flow chrome ─────────────────────────────────────────────
+   The library ships a generic grey control panel; these bring it onto the
+   app's own palette and give the buttons a real touch target. */
+.orgchart-canvas .react-flow__controls {
+  gap: 2px;
+  border-radius: var(--radius);
+  border: 1px solid var(--color-border);
+  background: #fff;
+  box-shadow: 0 2px 10px rgb(45 28 38 / 0.08);
+  overflow: hidden;
+}
+
+.orgchart-canvas .react-flow__controls-button {
+  width: 32px;
+  height: 32px;
+  border: none;
+  border-bottom: 1px solid var(--color-border-subtle);
+  background: #fff;
+  color: var(--color-ink-body);
+}
+
+.orgchart-canvas .react-flow__controls-button:last-child {
+  border-bottom: none;
+}
+
+.orgchart-canvas .react-flow__controls-button:hover {
+  background: var(--color-brand-100);
+  color: var(--color-brand-700);
+}
+
+.orgchart-canvas .react-flow__controls-button svg {
+  fill: currentColor;
+  max-width: 14px;
+  max-height: 14px;
+}
+
+.orgchart-canvas .react-flow__minimap {
+  border-radius: var(--radius);
+  border: 1px solid var(--color-border);
+  background: #fff;
+  box-shadow: 0 2px 10px rgb(45 28 38 / 0.08);
+}
+
+/* Node selection has to stay enabled (it is what gives the card pointer
+   events at all — see GraphOrgChart), but the card carries its own hover and
+   match styling, so React Flow's default selected/focus outline is noise. */
+.orgchart-canvas .react-flow__node.selected,
+.orgchart-canvas .react-flow__node:focus,
+.orgchart-canvas .react-flow__node:focus-visible {
+  outline: none;
+  box-shadow: none;
+}
+
+.orgchart-canvas .react-flow__attribution {
+  background: transparent;
+  font-size: 10px;
+}
+
+.orgchart-canvas .react-flow__attribution a {
+  color: var(--color-ink-muted);
+}
+
+/* The minimap costs more screen than it earns on a phone. */
+@media (max-width: 1023px) {
+  .orgchart-canvas .react-flow__minimap {
+    display: none;
+  }
 }