Refactor: Fix clippy warnings and introduce AppError

server/src/handlers/git.rs

@@ -27,11 +27,10 @@ impl McpTool for GetActiveWorktreeContextHandler {
             let repo = git2::Repository::discover(&cwd).map_err(|e| format!("Not in a git repository: {}", e))?;
             
             let mut branch_name = String::new();
-            if let Ok(head) = repo.head() {
-                if let Some(name) = head.shorthand() {
+            if let Ok(head) = repo.head()
+                && let Some(name) = head.shorthand() {
                     branch_name = name.to_string();
                 }
-            }
 
             let mut opts = git2::DiffOptions::new();
             let mut diff = None;