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.

actions/positions.ts

@@ -6,34 +6,39 @@ import { createClient } from "@/lib/supabase/server";
 
 type ActionResult = { success: boolean; error?: string };
 
+const POSITION_PATHS = ["/positions", "/orgchart", "/"];
+
+async function callRpc(
+  fn: "create_position" | "delete_position" | "staff_position_internally",
+  payload: Record<string, unknown>,
+  revalidate: string[]
+): Promise<ActionResult> {
+  const supabase = await createClient();
+  const { error } = await supabase.rpc(fn, { payload });
+  if (error) return { success: false, error: error.message };
+  for (const path of revalidate) revalidatePath(path);
+  return { success: true };
+}
+
 export async function createPosition(payload: {
   title: string;
   superior_employee_id: string;
   is_lead: boolean;
   team_id?: string;
+  valid_from: string;
 }): Promise<ActionResult> {
-  const supabase = await createClient();
-  const { error } = await supabase.rpc("create_position", { payload });
-  if (error) return { success: false, error: error.message };
-  revalidatePath("/positions");
-  revalidatePath("/orgchart");
-  revalidatePath("/");
-  return { success: true };
+  return callRpc("create_position", payload, POSITION_PATHS);
+}
+
+export async function deletePosition(positionId: string): Promise<ActionResult> {
+  return callRpc("delete_position", { position_id: positionId }, POSITION_PATHS);
 }
 
 export async function staffPositionInternally(payload: {
   position_id: string;
   employee_id: string;
 }): Promise<ActionResult> {
-  const supabase = await createClient();
-  const { error } = await supabase.rpc("staff_position_internally", { payload });
-  if (error) return { success: false, error: error.message };
-  revalidatePath("/positions");
-  revalidatePath("/orgchart");
-  revalidatePath("/employees");
-  revalidatePath(`/employees/${payload.employee_id}`);
-  revalidatePath("/");
-  return { success: true };
+  return callRpc("staff_position_internally", payload, [...POSITION_PATHS, "/employees", `/employees/${payload.employee_id}`]);
 }
 
 export type SuperiorSearchResult = { id: string; first_name: string; last_name: string; job_title: string; division_id: string };