Fix silent failures in whitelist add/remove operations

[Copilot]

Whitelist modifications were silently ignoring all failures, hiding network errors and authorization issues from users while still triggering UI refetches.

Changes

• Handle HTTP responses: Check resp.ok() before refetching whitelist data
• Log failures: Use console::error_1 to surface HTTP errors and network failures
• Conditional refetch: Only update UI state on successful operations

// Before: silent failure, always refetch
let _ = builder.send().await;
whitelist_resource.refetch();

// After: log errors, conditional refetch
match builder.send().await {
    Ok(resp) => {
        if resp.ok() {
            whitelist_resource.refetch();
        } else {
            web_sys::console::error_1(&JsValue::from_str(&format!(
                "Failed to add URL to whitelist: HTTP {}", resp.status()
            )));
        }
    }
    Err(e) => {
        web_sys::console::error_1(&JsValue::from_str(&format!(
            "Failed to add URL to whitelist: {:?}", e
        )));
    }
}

Applies to both add_whitelist_item and remove_whitelist_item actions in client/src/pages/view.rs.

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