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/bridge.js

@@ -15,6 +15,8 @@ export const get = (path) => api("GET", path)
 export const post = (path, body) => api("POST", path, body ?? {})
 export const patch = (path, body) => api("PATCH", path, body)
 export const del = (path) => api("DELETE", path)
+/** A `GET` on /api/v2 that answers plain text (a shown file). Rejects with {status, detail}. */
+export const getText = (path) => invoke("api_text", { path })
 
 /** An error's words, whatever shape it came in. */
 export function why(err) {