refactor(credentials): remove credential expiry support and API

The credential expiry feature has been removed from both the Rust
backend and the frontend. Stored credentials now include only
username and password.

- Remove expiresAt field from StoredCredential
- Simplify API by removing expiry param from credSave
- Drop expiry UI and expiry checks across the app

src-tauri/src/git.rs

@@ -2432,8 +2432,6 @@ const CRED_SERVICE: &str = "tauri_git_lite";
 pub struct StoredCredential {
     pub username: String,
     pub password: String,
-    #[serde(default, rename = "expiresAt", skip_serializing_if = "Option::is_none")]
-    pub expires_at: Option<String>,
 }
 
 fn cred_entry(key: &str) -> Result<keyring::Entry, String> {
@@ -2616,19 +2614,9 @@ pub fn cred_load(key: String) -> Result<Option<StoredCredential>, String> {
 }
 
 #[tauri::command(async)]
-pub fn cred_save(
-    key: String,
-    username: String,
-    password: String,
-    expires_at: Option<String>,
-) -> Result<(), String> {
+pub fn cred_save(key: String, username: String, password: String) -> Result<(), String> {
     let entry = cred_entry(&key)?;
-    let expires_at = expires_at.filter(|value| !value.trim().is_empty());
-    let cred = StoredCredential {
-        username,
-        password,
-        expires_at,
-    };
+    let cred = StoredCredential { username, password };
     let json = serde_json::to_string(&cred)
         .map_err(|err| format!("Could not serialize credentials: {err}"))?;
     entry