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)/employees/[id]/page.tsx

@@ -11,23 +11,35 @@ export default async function EmployeeDetailPage({ params }: PageProps) {
   const { data: employee } = await supabase.from("employees").select("*").eq("id", id).single();
   if (!employee) notFound();
 
-  const [{ data: manager }, { data: directReports }, { data: history }, { data: divisions }, { data: departments }, { data: teams }, { data: locations }, { data: openPositions }] =
-    await Promise.all([
-      employee.manager_id
-        ? supabase.from("employees").select("id, first_name, last_name, job_title").eq("id", employee.manager_id).single()
-        : Promise.resolve({ data: null }),
-      supabase
-        .from("employees")
-        .select("id, first_name, last_name, job_title, status")
-        .eq("manager_id", id)
-        .order("last_name"),
-      supabase.from("employee_history").select("*").eq("employee_id", id).order("event_date", { ascending: false }).order("created_at", { ascending: false }),
-      supabase.from("divisions").select("*").order("name"),
-      supabase.from("departments").select("*"),
-      supabase.from("teams").select("*"),
-      supabase.from("locations").select("*").order("name"),
-      supabase.from("positions").select("id, position_number, title, team_id, is_lead").eq("status", "open"),
-    ]);
+  const [
+    { data: manager },
+    { data: directReports },
+    { data: history },
+    { data: dependents },
+    { data: notes },
+    { data: divisions },
+    { data: departments },
+    { data: teams },
+    { data: locations },
+    { data: openPositions },
+  ] = await Promise.all([
+    employee.manager_id
+      ? supabase.from("employees").select("id, first_name, last_name, job_title").eq("id", employee.manager_id).single()
+      : Promise.resolve({ data: null }),
+    supabase
+      .from("employees")
+      .select("id, first_name, last_name, job_title, status")
+      .eq("manager_id", id)
+      .order("last_name"),
+    supabase.from("employee_history").select("*").eq("employee_id", id).order("event_date", { ascending: false }).order("created_at", { ascending: false }),
+    supabase.from("employee_dependents").select("*").eq("employee_id", id).order("created_at"),
+    supabase.from("employee_notes").select("*").eq("employee_id", id).order("created_at", { ascending: false }),
+    supabase.from("divisions").select("*").order("name"),
+    supabase.from("departments").select("*"),
+    supabase.from("teams").select("*"),
+    supabase.from("locations").select("*").order("name"),
+    supabase.from("positions").select("id, position_number, title, team_id, is_lead").eq("status", "open"),
+  ]);
 
   return (
     <EmployeeDetail
@@ -35,6 +47,8 @@ export default async function EmployeeDetailPage({ params }: PageProps) {
       manager={manager ?? null}
       directReports={directReports ?? []}
       history={history ?? []}
+      dependents={dependents ?? []}
+      notes={notes ?? []}
       divisions={divisions ?? []}
       departments={departments ?? []}
       teams={teams ?? []}