feat(docker): take run-mode availability from the container

The run-mode dropdown hides CLIs that are not installed on the HOST (#201). That
is right for local sessions and wrong for a container case, whose agents run
inside the container: a host with no claude installed hides the mode while the
container ships one, which is exactly what happened on a real deployment.

The adoption preflight already probes what the container has, so that result is
persisted on the case and surfaced through CaseInfo. Docker cases gate on it;
every other case keeps the host probe unchanged.

An absent list reads as "do not gate" rather than "nothing available": an owned
container runs our base image, which ships every CLI, and treating unknown as
empty would leave the menu with Shell alone.

src/types/api.ts

@@ -167,6 +167,13 @@ export interface CaseInfo {
     image?: string;
     path: string;
     network?: string;
+    /**
+     * CLIs available INSIDE the container. A container case runs its agents in
+     * the container, so HOST CLI availability says nothing about what it can
+     * run. Absent = unknown (an owned container runs our base image, which ships
+     * every CLI), which the UI reads as "do not gate".
+     */
+    availableModes?: string[];
   };
 }