feat: add level schema and tilemap tests

- Introduced a JSON schema for game levels to validate level data structure.
- Added comprehensive tests for tilemap functionalities including collision resolution, tile type retrieval, and level loading.
- Enhanced the SyncSystem to manage remote state synchronization and interpolation for smoother gameplay.
- Implemented an AudioSystem with tests to ensure audio loading and playback functionality.
- Updated NetworkClient to support dynamic WebSocket URLs from environment variables.
- Added integration tests for matchmaking and network communication between clients.
- Improved RenderSystem to correctly render player nicknames above sprites.

Co-authored-by: Copilot <copilot@github.com>

public/levels/level.schema.json

@@ -0,0 +1,72 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "LevelData",
+  "description": "Schema for Zamny Browser game levels",
+  "type": "object",
+  "properties": {
+    "width": {
+      "description": "Width of the level in tiles",
+      "type": "integer",
+      "minimum": 1
+    },
+    "height": {
+      "description": "Height of the level in tiles",
+      "type": "integer",
+      "minimum": 1
+    },
+    "tileSize": {
+      "description": "Size of each tile in pixels (e.g. 32)",
+      "type": "integer",
+      "minimum": 1
+    },
+    "tiles": {
+      "description": "Flat array of tile types (0=walkable, 1=wall, 2=water, 3=door)",
+      "type": "array",
+      "items": {
+        "type": "integer",
+        "minimum": 0,
+        "maximum": 3
+      }
+    },
+    "spawnPoints": {
+      "description": "Locations where players can spawn",
+      "type": "array",
+      "items": {
+        "type": "object",
+        "properties": {
+          "x": {
+            "type": "number"
+          },
+          "y": {
+            "type": "number"
+          }
+        },
+        "required": ["x", "y"]
+      }
+    },
+    "entities": {
+      "description": "Entities to spawn in the level (enemies, items, etc.)",
+      "type": "array",
+      "items": {
+        "type": "object",
+        "properties": {
+          "type": {
+            "type": "string"
+          },
+          "x": {
+            "type": "number"
+          },
+          "y": {
+            "type": "number"
+          },
+          "props": {
+            "type": "object",
+            "additionalProperties": true
+          }
+        },
+        "required": ["type", "x", "y"]
+      }
+    }
+  },
+  "required": ["width", "height", "tileSize", "tiles"]
+}