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/index.html

@@ -2838,8 +2838,9 @@
             </div>
             <div class="form-row docker-adopt-only">
               <label>Container Name</label>
-              <input type="text" id="dockerContainerName" placeholder="my-dev-box" pattern="[a-zA-Z0-9][a-zA-Z0-9_.-]+" autocomplete="off" autocapitalize="off" spellcheck="false">
-              <span class="form-hint">Must be running already. <button type="button" class="btn-inline-check" id="dockerAdoptCheckBtn">Check container</button></span>
+              <input type="text" id="dockerContainerName" list="dockerContainerList" placeholder="my-dev-box" pattern="[a-zA-Z0-9][a-zA-Z0-9_.-]+" autocomplete="off" autocapitalize="off" spellcheck="false">
+              <datalist id="dockerContainerList"></datalist>
+              <span class="form-hint">Pick from the running containers or type a name. <button type="button" class="btn-inline-check" id="dockerAdoptCheckBtn">Check container</button></span>
             </div>
             <div class="form-row docker-adopt-only">
               <label>Container Workdir</label>