Aside REPL file uploads: fetch into session dir first

Aside's aside repl sandboxes fs and setInputFiles to the session directory (global pwd, a string), so setInputFiles('/abs/path') fails with 'escapes the session directory'. Workaround inside one REPL call: serve the file on 127.0.0.1 (python3 -m http.server), fetch() it, write it to path.join(pwd, name), then setInputFiles on that path. Also: tabs created with openTab() in a one-shot aside repl "..." close when the call ends; open a persistent tab with aside "https://url" and re-attach via attachBrowserTab(targetId). Locator API is partial (no getByPlaceholder/allInnerTexts/count on xpath), so parse snapshot refs instead.