fix(auth): trim the username before authenticating

The login form guarded on `username.trim()` but sent the raw value, so a
trailing space from a soft keyboard reached the server verbatim. Jellyfin
reports that as an unknown user, which surfaces as a 401 indistinguishable
from a wrong password — the user is certain of their credentials and the app
insists otherwise.

Normalising in AuthManager rather than the form keeps it on the path every
caller uses, alongside normalize_url. Only surrounding whitespace is
stripped; interior spaces are legal in Jellyfin usernames.

src-tauri/src/auth/mod.rs

@@ -129,6 +129,18 @@ impl AuthManager {
         Ok(normalized)
     }
 
+    /// Normalize a username before it goes to the server.
+    ///
+    /// Only surrounding whitespace is stripped — interior spaces are legal in
+    /// Jellyfin usernames. Without this, a trailing space from a soft keyboard's
+    /// autocorrect makes the server report an unknown user, which surfaces as a
+    /// 401 that looks exactly like a wrong password.
+    ///
+    /// TRACES: UR-042 | DR-054
+    pub fn normalize_username(username: &str) -> String {
+        username.trim().to_string()
+    }
+
     /// Connect to server and get server info
     pub async fn connect_to_server(&self, server_url: &str) -> Result<ServerInfo, String> {
         let normalized_url = Self::normalize_url(server_url)?;
@@ -185,6 +197,7 @@ impl AuthManager {
     ) -> Result<AuthResult, String> {
         let url = Self::normalize_url(server_url)?;
         let endpoint = format!("{}/Users/AuthenticateByName", url);
+        let username = Self::normalize_username(username);
 
         log::info!("[AuthManager] Authenticating user: {}", username);
 
@@ -443,6 +456,26 @@ mod tests {
         );
     }
 
+    /// Usernames must be trimmed before they reach the server: the Android soft
+    /// keyboard appends a trailing space after autocorrect, and Jellyfin then
+    /// reports an unknown user — a 401 indistinguishable from a wrong password.
+    #[test]
+    fn test_normalize_username_trims_whitespace() {
+        assert_eq!(AuthManager::normalize_username("duncan "), "duncan");
+        assert_eq!(AuthManager::normalize_username(" duncan"), "duncan");
+        assert_eq!(AuthManager::normalize_username("  duncan  "), "duncan");
+        assert_eq!(AuthManager::normalize_username("duncan\n"), "duncan");
+    }
+
+    /// Interior spaces are legal in Jellyfin usernames and must survive.
+    #[test]
+    fn test_normalize_username_preserves_interior_spaces() {
+        assert_eq!(
+            AuthManager::normalize_username("  duncan tourolle  "),
+            "duncan tourolle"
+        );
+    }
+
     /// Test URL normalization - real world case
     #[test]
     fn test_normalize_url_real_world_case() {