fix: fog-of-war entities, multi-level descend feedback, camera centering, fewer levels

- FOG: sceneFromGameState only emits exit/entrance/treasure/items once their cell is EXPLORED,
  and the monster only while IN VIEW — no more exit stairs leaking through the fog.
- DESCEND FEEDBACK: reaching a non-final exit descends (multi-level) and used to silently dump the
  player at a new entrance (read as a bug). Server now sends depth/maxDepth on game_event; the
  client shows "Stairs down! Level N of M — keep going". Also lowered level counts (WOW 4->2,
  BTC 8->3, XMR 2->1) — clearing 4-8 levels in one block was unwinnable; kept modest until proper
  multi-level calibration + UX.
- CAMERA: the host filled the very-tall #game-display so centering put the player low; it's now a
  bounded viewport (min(100%,78vh)) centered in #game-display, so the player stays on-screen-centered.
Suite 62/435 green.

src/game/difficultyConfig.js

@@ -157,12 +157,15 @@ function getDifficultyPreset(cryptoType = 'WOW', overridePreset = null) {
 // NOTE: the exact per-network level counts are sim starting points (calibration re-run is pending
 // the sim's multi-level support). Operator env overrides (DUNGEON_LEVELS, DUNGEON_*, MONSTER_*) win.
 // Kill: NETWORK_TUNING_DISABLED=true.
+// Level counts trimmed from the first sim estimate — 4-8 levels in a single block deadline is too
+// punishing (you rarely clear them all before the block). Kept modest until a real multi-level
+// calibration run + the descent UX are in. Reach-exit-to-win stays intuitive with fewer levels.
 const NETWORK_TUNING = {
     GRIN: { levels: 1 }, // ~1 min blocks
-    XMR:  { levels: 2 }, // ~2 min
+    XMR:  { levels: 1 }, // ~2 min
     LTC:  { levels: 2 }, // ~2.5 min
-    WOW:  { levels: 4 }, // ~5 min (measured)
-    BTC:  { levels: 8 }  // ~10 min
+    WOW:  { levels: 2 }, // ~5 min (measured)
+    BTC:  { levels: 3 }  // ~10 min
 };
 
 // Fold the per-network level count onto the resolved preset (size + monster stay at the preset).

src/game/movementManager.js

@@ -65,9 +65,12 @@ class MovementManager {
       this.spectatorManager.broadcastToSpectators(game.id, state);
     }
 
-    // Handle special events from moveResult (escape / treasure)
+    // Handle special events from moveResult (escape / treasure / descend). Include depth for the
+    // multi-level descend so the client can tell the player they took the stairs down (not a bug).
     if (moveResult && moveResult.event) {
-      this.io.to(socketId).emit('game_event', { event: moveResult.event });
+      this.io.to(socketId).emit('game_event', {
+        event: moveResult.event, depth: moveResult.depth, maxDepth: moveResult.maxDepth
+      });
     }
   }