fix(plugins): draft metadata survives a remount, plugin commands follow the composer lock

Draft metadata was component state while the prompt lived in the draft store, so a composer that
remounted across the compact breakpoint kept its text and lost the plugin's choices. It now lives
in the draft store beside the prompt, is cleared when the draft is sent, and is not cleared when
the prompt is emptied. It is not persisted across app restarts.

While the New workspace composer is creating the agent, the built-in controls are disabled but
plugin controls and commands were not. They read the composer's own lock: Paseo controls render
disabled, and setPrompt, insertText and the agent commands refuse.

The options and metadata a plugin reads are frozen copies, through the same helper the timeline
projection uses. The composer control test mounted components in JSDOM, which the testing rules
ban; it now runs in the browser project.

packages/app/src/plugins/react-native/composer-controls.tsx

@@ -5,6 +5,7 @@ import {
   useComposerControlSurface,
   type ComposerControlItem,
 } from "@/composer/agent-controls/composer-control";
+import { useComposerLocked } from "@/composer/session";
 import { parsePluginIcon, pluginIconComponent } from "../icons";
 
 /** Icons resolve at render, so an invalid one throws to the item's boundary. */
@@ -21,12 +22,13 @@ function PluginComposerControl({
   disabled: boolean | undefined;
 }) {
   const surface = useComposerControlSurface();
+  const locked = useComposerLocked();
   const [open, setOpen] = useState(false);
   return (
     <ComposerControl
       item={item}
       surface={surface}
-      disabled={disabled}
+      disabled={disabled || locked}
       open={open}
       onOpenChange={setOpen}
     />