build: switch from yarn to npm to manage js dependencies and move js contents to root

yarn v1 is being deprecated and starts to have some issues

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

config/dev.exs

@@ -16,7 +16,6 @@ config :mobilizon, Mobilizon.Web.Endpoint,
   watchers: [
     node: [
       "node_modules/.bin/vite",
-      cd: Path.expand("../js", __DIR__)
     ]
   ]
 

config/e2e.exs

@@ -16,7 +16,7 @@ config :mobilizon, Mobilizon.Web.Endpoint,
   check_origin: false,
   # Somehow this can't be merged properly with the dev config so we got this…
   watchers: [
-    yarn: [cd: Path.expand("../js", __DIR__)]
+    npm: []
   ]
 
 config :vite_phx,