Refactor texture handling and update route structure

Moved sessionserver routes to correct directory and removed subdirectory logic from texture file lookup. Updated texture URLs to remove leading slashes and fixed endpoint concatenation. Added default textures for Alex and Steve.

services/userService.js

@@ -459,7 +459,7 @@ async function uploadSkin(uuid, fileObject, variant) {
             await fs.writeFile(targetPath, buffer)
 
             const newTextureUuid = crypto.randomUUID()
-            const textureUrl = `/texture/${hash}`
+            const textureUrl = `texture/${hash}`
             await userRepository.createTexture(newTextureUuid, hash, 'SKIN', textureUrl, null)
         }