feat: ship docker as a first-party in-process plugin

Moves docker backend and frontend into plugins/docker/, alongside
ssh-terminal. Adds a host editor tab seam, a dashboard card registry,
and a build step to compile plugin backends into dist.

plugins/docker/frontend/DockerApp.tsx

@@ -0,0 +1,53 @@
+import React from "react";
+import { useTranslation } from "react-i18next";
+import { DockerManager } from "./DockerManager.tsx";
+import { FullScreenAppWrapper } from "@/features/FullScreenAppWrapper.tsx";
+import { ConnectionScreen } from "@/components/connection/ConnectionScreen.tsx";
+
+interface DockerAppProps {
+  hostId?: string;
+}
+
+const DockerApp: React.FC<DockerAppProps> = ({ hostId }) => {
+  const { t } = useTranslation();
+  return (
+    <FullScreenAppWrapper hostId={hostId}>
+      {(hostConfig, phase) => {
+        if (phase === "loading") {
+          return (
+            <div className="relative h-full w-full">
+              <ConnectionScreen
+                status="connecting"
+                message={t("hosts.loadingHost")}
+              />
+            </div>
+          );
+        }
+
+        if (!hostConfig) {
+          return (
+            <div className="relative h-full w-full">
+              <ConnectionScreen
+                status="disconnected"
+                message={t("hosts.hostNotFound")}
+              />
+            </div>
+          );
+        }
+
+        return (
+          <DockerManager
+            hostConfig={hostConfig}
+            title={hostConfig.name || `${hostConfig.username}@${hostConfig.ip}`}
+            isVisible={true}
+            isTopbarOpen={false}
+            embedded={true}
+            onClose={() => {}}
+          />
+        );
+      }}
+    </FullScreenAppWrapper>
+  );
+};
+
+export default DockerApp;