Studio: IME / multilingual composer regression test + RTL dir="auto" (unslothai#5485)

Adds dir="auto" to the main, edit, and compare chat composers so RTL
scripts (Arabic, Hebrew, Persian, Urdu) flow right to left without
forcing the rest of the UI into RTL. Wires a model-free Playwright
smoke (multilingual paste round trip across 31 scripts + a stuck-IME
composition repro for issue unslothai#5318 / PR unslothai#5327) into the Studio UI CI
job as a third Studio boot, plus a pure-Python static-guard test that
locks down dir="auto" on all three composers and the minimal env
contract for the smoke.

Author: danielhanchen