Feature Request: Support custom basePath (subpath deployment) for HyperDX UI

### Description
Currently, the HyperDX UI is deployed assuming access at the root ("/") path. In deployments behind a reverse proxy or ingress under a subpath (e.g., `https://example.com/observe/`), asset paths like `/_next/static/...` break, causing UI rendering issues.

### Proposal
Add Helm chart support to configure a custom base path, such as:

```yaml
hyperdx:
basePath: "/observe"
```

### This would:

- Set the Next.js basePath and assetPrefix appropriately.
- Adjust redirect logic to use the configured subpath.
- Allow the application to function correctly when served under paths other than /.

### Justification

Many deployments are used behind reverse proxies with path-based routing. In these scenarios, being able to configure a custom base path is essential to ensure that the UI works as expected. This functionality would be highly appreciated by users who need to integrate HyperDX alongside other services on the same domain.

### References

Next.js basePath documentation: https://nextjs.org/docs/pages/api-reference/next-config-js/basePath