Add members/invitations and code-based gateway setup to the Setup page

Gateway setup shows a `continuum-proxy enrol` command with a one-time
code; the manual settings stay behind "Set it up by hand". New members
section for inviting by email, plus an /invite page to accept, and the
login page honours a safe `next` redirect.

packages/ui/src/components/GatewaySetup.vue

@@ -1,6 +1,6 @@
 <script setup lang="ts">
 import { computed, ref } from "vue";
-import type { AppFarm } from "../types";
+import type { AppFarm, EnrolmentCode } from "../types";
 
 const props = defineProps<{
   farm: AppFarm;
@@ -10,8 +10,39 @@ const props = defineProps<{
   uplinkUrl: string;
   /** Mints a new proxy token. Rejects with a readable message. */
   mint: () => Promise<string>;
+  /** Makes a one-time enrolment code. Rejects with a readable message. */
+  enrol: () => Promise<EnrolmentCode>;
+  /** The API's address as a gateway reaches it, for the enrol command. */
+  apiUrl: string;
 }>();
 
+const enrolment = ref<EnrolmentCode | null>(null);
+const enrolBusy = ref(false);
+const enrolCopied = ref(false);
+const command = computed(() => `continuum-proxy enrol ${props.apiUrl} ${enrolment.value?.code ?? ""}`);
+
+async function makeCode() {
+  enrolBusy.value = true;
+  failure.value = "";
+  try {
+    enrolment.value = await props.enrol();
+    enrolCopied.value = false;
+  } catch (err) {
+    failure.value = err instanceof Error ? err.message : String(err);
+  } finally {
+    enrolBusy.value = false;
+  }
+}
+
+async function copyCommand() {
+  try {
+    await navigator.clipboard.writeText(command.value);
+    enrolCopied.value = true;
+  } catch {
+    enrolCopied.value = false;
+  }
+}
+
 const token = ref("");
 const confirming = ref(false);
 const busy = ref(false);
@@ -68,6 +99,23 @@ async function copy() {
       settings below.
     </p>
 
+    <div class="gateway-setup__enrol">
+      <template v-if="!enrolment">
+        <button type="button" :disabled="enrolBusy" @click="makeCode">Connect a gateway with a code</button>
+      </template>
+      <template v-else>
+        <p>
+          On the computer that will run the gateway, run this within 15 minutes. The code works once, and it does not
+          replace a gateway that is already connected.
+        </p>
+        <pre class="gateway-setup__settings">{{ command }}</pre>
+        <button type="button" @click="copyCommand">{{ enrolCopied ? "Copied" : "Copy" }}</button>
+        <button type="button" @click="enrolment = null">Done</button>
+      </template>
+    </div>
+
+    <details class="gateway-setup__manual">
+      <summary>Set it up by hand instead</summary>
     <template v-if="!token">
       <button v-if="!confirming" type="button" :disabled="busy" @click="start">
         {{ gatewayOnline ? "Create a new gateway token" : "Create gateway settings" }}
@@ -91,6 +139,7 @@ async function copy() {
       <button type="button" @click="copy">{{ copied ? "Copied" : "Copy" }}</button>
       <button type="button" @click="token = ''">Done</button>
     </template>
+    </details>
 
     <p v-if="failure" role="alert" class="gateway-setup__error">{{ failure }}</p>
   </section>