Full-screen map with draggable, collapsible floating HUD windows

- MapLibre map is now a fixed, full-viewport background layer (z-0)
- New FloatingWindow: drag by title bar (pointer capture, viewport-clamped,
  position persisted to localStorage), collapsible to title bar, bring-to-front
  z-index; semi-transparent slate window with amber/cyan accents
- Game screen re-laid out as floating windows over the map: slim top header
  (scenario, turn + date, player nation chip, Idle/Simulating status, Focus map
  collapse-all), dossier (top-left), event feed (right), Your move deck
  (bottom-center), legend (bottom-left), tiny zoom control (bottom-right)
- MapLibre default nav controls removed; custom floating zoom-in/out control
- Panels gain an inWindow mode (no card chrome, same testids)
- server: honor HISTORY_API_PORT as PORT fallback (dev proxy/e2e agreement)
- css: keep maplibre canvas base color and Radix portals above HUD windows

src/components/MapLegend.tsx

@@ -0,0 +1,32 @@
+import type { RegionMap } from '@shared/protocol';
+
+/**
+ * Small bottom-left legend mapping each nation on the map to its stable color.
+ * Rendered by the game screen as a minimal floating window over the map.
+ */
+export default function MapLegend({ regions }: { regions: RegionMap }) {
+  const owners = new Map<string, { color: string; owner: string }>();
+  for (const r of Object.values(regions)) {
+    if (r.ownerId && !owners.has(r.ownerId)) owners.set(r.ownerId, { color: r.color, owner: r.owner });
+  }
+  const list = [...owners.entries()].sort((a, b) => a[1].owner.localeCompare(b[1].owner));
+  if (list.length === 0) return null;
+  return (
+    <div
+      data-testid="map-legend"
+      className="max-h-[52vh] overflow-y-auto p-2.5"
+    >
+      <div className="mb-1.5 text-[10px] font-semibold uppercase tracking-widest text-muted-foreground">
+        Nations
+      </div>
+      <ul className="space-y-1">
+        {list.map(([id, o]) => (
+          <li key={id} data-testid="map-legend-item" className="flex items-center gap-1.5 text-xs">
+            <span className="inline-block size-2.5 shrink-0 rounded-sm" style={{ background: o.color }} />
+            <span className="truncate">{o.owner}</span>
+          </li>
+        ))}
+      </ul>
+    </div>
+  );
+}