fix!(lua.endpoints): allow sell of jokers/consumables during BLIND_SELECT

The `sell` endpoint rejects valid sales during `BLIND_SELECT` that the game permits. Verified against `vendors/lovely/dump/` and confirmed empirically.

## Bug

`src/lua/endpoints/sell.lua` `requires_state` omits `BLIND_SELECT`, so selling a joker or consumable during blind selection returns `INVALID_STATE`. The game allows it: `Card:can_sell_card` (`card.lua:1896` in the dump) has the `BLIND_SELECT` guard **commented out**.

Empirical: sold a joker during blind select → money 30→31, joker removed, state stayed `BLIND_SELECT`.

## Fix

Add `G.STATES.BLIND_SELECT` to `requires_state` **and** the completion-detection `valid_state` whitelist (~L150). Both must change or the endpoint hangs.

Sibling of #202.