fix: added ui indicator on how apikeys are set (UI/Env) for api-key-manager component (#732)

* fixed #333

* Added instruction in case api-key is not set.

* addressed some of the review changes:

1. moved function definiton to useCallback.
2. added a cache to store the env key status and the api call is made only on a cache miss.

* Manages the API-key entered via UI in a better way.

- Persist API keys in cookies when entered via UI
- Automatically load saved keys when switching between providers
- Preserve existing functionality for environment variable based keys

* Re-used map from utils/constants file.

* Code cleanup -  Removed redundant API key init in BaseChat as its already handled by APIKeyManager component.

app/routes/api.check-env-key.ts

@@ -0,0 +1,16 @@
+import type { LoaderFunction } from '@remix-run/node';
+import { providerBaseUrlEnvKeys } from '~/utils/constants';
+
+export const loader: LoaderFunction = async ({ context, request }) => {
+  const url = new URL(request.url);
+  const provider = url.searchParams.get('provider');
+
+  if (!provider || !providerBaseUrlEnvKeys[provider].apiTokenKey) {
+    return Response.json({ isSet: false });
+  }
+
+  const envVarName = providerBaseUrlEnvKeys[provider].apiTokenKey;
+  const isSet = !!(process.env[envVarName] || (context?.cloudflare?.env as Record<string, any>)?.[envVarName]);
+
+  return Response.json({ isSet });
+};