Fix inventory window never refreshing live (per-character version)

The inventoryVersion counter in useLiveData was a single global value that
bumped on every inventory_delta for any character. With 60+ active chars
all generating deltas, the global counter advanced multiple times per
second.

InventoryWindow's debounce effect watched this global counter, so every
bump reset its 2-second fetch timer. Since bumps arrived faster than 2s,
the fetch never fired — the window appeared frozen until the user closed
and reopened it (which triggered the initial-fetch effect).

Fix: make inventoryVersions a Map<string, number> keyed by character name.
Each inventory_delta now only bumps its own character's counter, so an
open window's debounce correctly fires 2s after its character's last
delta, ignoring unrelated traffic.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/map/MapLayout.tsx

@@ -66,7 +66,7 @@ export const MapLayout: React.FC<Props> = ({ data }) => {
           selectedPlayer={selectedPlayer}
         />
         <WindowRenderer characters={data.characters} chatMessages={data.chatMessages}
-          nearbyObjects={data.nearbyObjects} inventoryVersion={data.inventoryVersion}
+          nearbyObjects={data.nearbyObjects} inventoryVersions={data.inventoryVersions}
           equipmentCantrips={data.equipmentCantrips} characterStats={data.characterStats}
           socket={data.socketRef.current} />
         <RareNotification recentRares={data.recentRares} />