Strip trailing slash from API URL to prevent double slashes

Fixes issue where API URL like 'https://towerops.net/' would result in
URLs like 'https://towerops.net//api/v1/agent/config' causing 406 errors.

src/api_client.rs

@@ -46,6 +46,8 @@ pub struct ApiClient {
 impl ApiClient {
     /// Create a new API client
     pub fn new(base_url: String, token: String) -> Result<Self> {
+        // Strip trailing slash from base_url to avoid double slashes in URLs
+        let base_url = base_url.trim_end_matches('/').to_string();
         Ok(Self { base_url, token })
     }