fix: include server/static in published package files (#1113)

The sandbox_proxy.html file was not shipped in the npm package because
the files arrays in both package.json and server/package.json only
included the build directory. The server code resolves the file via
join(__dirname, '..', 'static', 'sandbox_proxy.html') which expects
static/ as a sibling of build/, but it was missing from the package.

package.json

@@ -14,6 +14,7 @@
     "client/bin",
     "client/dist",
     "server/build",
+    "server/static",
     "cli/build"
   ],
   "workspaces": [

server/package.json

@@ -12,6 +12,7 @@
   },
   "files": [
     "build",
+    "static",
     "LICENSE"
   ],
   "scripts": {