fix: convert cf-kv and excalidraw-libraries from submodules to regular files

- Remove stale cloudflare-worker submodule entry from .gitmodules
- Remove .git dirs from cf-kv and excalidraw-libraries so Git tracks them as regular files
- Fixes 'No url found for submodule path cf-kv' CI error

excalidraw-libraries/vercel.json

@@ -0,0 +1,13 @@
+{
+  "headers": [
+    {
+      "source": "/(.*)\\.(png|jpg|jpeg|svg)",
+      "headers": [
+        {
+          "key": "Cache-Control",
+          "value": "public, max-age=2592000"
+        }
+      ]
+    }
+  ]
+}