fix: encode URL client-side to prevent double-slash normalization

[jansonjustin]

Fix: encode target URL client-side to prevent double-slash normalization

Closes #75

Problem

When a user submits a URL through the web UI, the form navigates to /<target_url> as a raw path. Browsers and reverse proxies (nginx, Traefik, Apache) normalize // in paths per RFC 3986, collapsing https:// to https:/. By the time the request reaches Ladder, the hostname is gone and it errors with http: no Host in request URL.

The existing workarounds (nginx merge_slashes off, Traefik sanitizePath: false, pinning Traefik to v3.3.5) are fragile and proxy-specific.

Fix

Encode the target URL with encodeURIComponent in the submit handler before navigation, so the browser never sees a raw :// in the path. decodeURIComponent is applied first to avoid double-encoding URLs that are already partially encoded (e.g. containing %20). A try/catch handles the edge case of malformed percent sequences.

try {
    url = encodeURIComponent(decodeURIComponent(url));
} catch (e) {
    url = encodeURIComponent(url);
}

This fix is proxy-agnostic and requires no configuration changes on the server side.