feat(docker): make the container field a picker you can also type into

Typing a container name from memory is error-prone. The field becomes a native
datalist: pick from the engine's containers, type to filter, or type a name that
is not listed (the engine may be remote, or the container may not exist yet).
A datalist gives all three natively, so no dropdown state machine is introduced.

Adds listDockerContainers and GET /api/docker-hosts/:hostId/containers, following
the listRemoteCodemanSessions discovery precedent: read-only and never throwing,
so an unreachable daemon returns an empty list and the field degrades to plain
text instead of erroring.

Stopped containers stay in the list, sorted after running ones and labelled.
Attaching does require a running container, but hiding stopped ones turns "my
container is not in the list" into a dead end, while showing
`Exited (137) 8 days ago` says exactly what to fix.

src/web/public/i18n.js

@@ -717,7 +717,7 @@
     'On: Codeman only runs docker exec into a container you already built and run — it never creates, starts, stops or removes it. The CLIs must already be installed and logged in inside it.':
       '开启后，{name}只会 docker exec 进入你自己构建并运行的容器，绝不创建、启动、停止或删除它；容器内必须已安装并登录好相应 CLI。',
     'Container Name': '容器名称',
-    'Must be running already.': '该容器必须已在运行。',
+    'Pick from the running containers or type a name.': '从正在运行的容器中选择，或直接输入名称。',
     'Check container': '检查容器',
     'Container Workdir': '容器内工作目录',
     'A path that already exists inside the container. Adoption mounts nothing, so this need not match the host workspace path.':