Remove invalid --directory flag that broke agent spawning

The --directory flag does not exist in Claude Code CLI. It was added in
c169cfc but caused every agent spawn to exit immediately with "unknown
option", resulting in Session: None errors. The process cwd (set via
cmd.cwd()) already correctly pins agents to the worktree directory.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/config.rs

@@ -226,11 +226,6 @@ impl ProjectConfig {
             args.push(render(sp));
         }
 
-        // Explicitly set the project directory so Claude Code doesn't
-        // resolve the main checkout via .git worktree indirection.
-        args.push("--directory".to_string());
-        args.push(worktree_path.to_string());
-
         Ok((command, args, prompt))
     }
 }
@@ -395,8 +390,7 @@ max_turns = 0
             .render_agent_args("/tmp/wt", "42_foo", None, None)
             .unwrap();
         assert_eq!(cmd, "claude");
-        assert!(args.contains(&"--directory".to_string()));
-        assert!(args.contains(&"/tmp/wt".to_string()));
+        assert!(args.is_empty());
         assert!(prompt.contains("42_foo"));
     }