ECS branch: parameters panel drops the Hide input affordance, and the hideInput locale key survives only in it

Two things on `components/rightSidePanel/parameters/WidgetActions.vue`, verified at PR #14246 head `907ca2b1479381eff7a617e656c9002806b5fa15`.

## 1. Orphaned `hideInput` locale key in `it`

The key was deleted from 13 of the 14 locales and left behind in Italian:

```
src/locales/it/main.json:3410: "hideInput": "Nascondi input"
```

`git grep hideInput -- src/locales` returns exactly that one hit; all 14 locales carry `showInput`. Key path is `rightSidePanel.hideInput`. Any locale key-diff check flags `it` as the odd one out from here on.

## 2. The "Hide input" affordance is gone from the parameters panel

`canToggleVisibility` became `canShowInput`, and `handleHideInput` plus the `demotePromotedInput` / `demoteWidget` calls are gone. What remains is a single `v-if="canShowInput"` button calling `handleShowInput()`.

Demotion is still reachable from `subgraph/SubgraphEditor.vue:281`, so the capability survives — but a user who promotes a widget from this panel can no longer un-promote it from the same menu.

Intentional, or fallout from the `parents[]` to `host` prop change? Either way it is a user-visible behaviour change with no changelog entry, and it is not in the compatibility audit.

Raised originally as a review thread on #14246; filed so the finding does not depend on that thread.