feat(ui): render the scene sharing dialogs and bar from a store

createSceneDialog keeps its builder but publishes the dialog's lines,
fields, buttons and status to a scene sharing store; SceneDialog.vue,
teleported to the body from the scene panels view, draws the same modal
with the same styles and opens it with Cancel focused. The EDIT DETAILS /
SHARE SCENE bar is drawn by that view while sharing offers it. The status
directive is shared with Provider Settings, and the two QA scripts that
drove the old DOM read the new dialog.

src/ui/rail/statusText.js

@@ -0,0 +1,14 @@
+/**
+ * Write a live region's message, even a repeated one, so a screen reader
+ * announces it again. The value is `{text, seq}`; the owner bumps `seq` for
+ * every message it says.
+ */
+export const vStatusText = {
+  mounted(el, { value }) {
+    el.textContent = value.text;
+  },
+  updated(el, { value, oldValue }) {
+    if (value.seq !== oldValue?.seq || value.text !== oldValue?.text)
+      el.textContent = value.text;
+  },
+};