kino_qx v0.3.0

Changed

• Kino.Qx.CredentialsCell now reevaluates on change and rebinds qx automatically. The cell is registered with reevaluate_on_change: true, so changing any persisted field (portal URL, region, backend, optimization level, shots) re-runs the cell and rebinds the notebook qx binding. Previously, picking a backend after Connect updated the generated code text but did not rebind qx until the user manually re-ran the cell — a downstream Kino.Qx.run!/2 would use a stale config. Visible behaviour change: editing a field now auto-re-runs the cell (on blur/commit, not per keystroke).
• The Smart Cell is now a guided 3-step sequence — (1) Livebook secrets, (2) Portal & region + Connect, (3) Job defaults. Step 3 is locked until Connect succeeds and shows a "pick a backend to finish" affordance until a backend is chosen. Pushed events, the __remembered__ saved-backend handling, and the privacy invariant (tokens never in cell state / .livemd) are unchanged.

Fixed

• An unconfigured cell no longer silently emits a broken config. With no backend chosen, to_source/1 previously emitted %Qx.Hardware.Config{… backend: "" …}, which failed downstream with no actionable message. It now emits a raise with a clear instruction ("select a backend …"). Combined with reevaluate_on_change, picking a backend flips the cell from this guard to a valid qx automatically.

Security

• to_source/1 re-validates optimization_level/shots before emitting them. A shared .livemd is plain text; a hand-crafted non-integer value would previously be interpolated verbatim into the generated cell source (which, with reevaluate_on_change, now auto-evaluates). Both fields are now routed through the existing validators with a safe fallback to the documented defaults, and the integer parsers reject trailing garbage.