One approval for app and agent; /api/v2 files and show; app_api 2

- The app's device login asks for `app models` and, where discovery says
  login.device.agent_scope, `agent_scope=models memory link` in the same
  approval. The agent's token goes to the bundled CLI on stdin
  (`lembas login --token-stdin --server <url> --json`) and is never kept
  here; if the CLI does not take it, it is given up on the server. A
  computer linked already keeps its link; a server without agent_scope
  gets the old two steps.
- The server pane reads GET /api/v2/files and /files/content (mounts open
  like folders; `withheld` shown in the server's words). The "not offered
  yet" state is gone.
- A show card's file comes from GET /api/v2/chats/{chat}/show?node=&version=
  or ?shown= as plain text (new `api_text` command, 1 MB cap); args.path is
  read only for agent chats on this computer, locally.
- The gate is link protocol 3 plus app_api 2 (APP_API = 2), not the
  server's version number, which says 1.7.2 on dev until its first beta.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ui/js/setup.js

@@ -1,7 +1,8 @@
 // Before the app: which server, and the app's sign-in to it. A server older than LLeMbas 2.0 is
 // refused here, with the reason Rust gave (src-tauri/src/server.rs, `check`). Signing in is the
 // server's device login: the approval page opens in the system's browser; this page shows the
-// code to compare and waits.
+// code to compare and waits. Where the server offers it (`one_approval`) and this computer is not
+// linked yet, the same approval links it for the agent: there is no second one.
 
 import { $, h, clear } from "./dom.js"
 import { invoke, listen, why } from "./bridge.js"
@@ -60,7 +61,8 @@ export function renderSetup(s) {
 
   if (s.discovery && !s.account) {
     const sign = h("section", { "aria-labelledby": "setup-sign-h" }, h("h2", { id: "setup-sign-h", text: t("Sign in") }))
-    sign.append(h("p", { class: "muted", text: t("The app signs in to your server once, in your browser, as any device does. It may then read and write your chats, as the web interface does.") }))
+    const both = s.discovery.one_approval && !s.linked
+    sign.append(h("p", { class: "muted", text: both ? t("The app signs in to your server once, in your browser, as any device does. It may then read and write your chats, as the web interface does, and the same approval links this computer for the agent.") : t("The app signs in to your server once, in your browser, as any device does. It may then read and write your chats, as the web interface does.") }))
     if (s.signing_in && code) {
       sign.append(
         h("p", null, t("Approve this code in the page that opened in your browser:")),