S7 review: align OAuth UI with S6's actual contract (server-26#225)

- complete: S6 returns streams_stopped, not stopped — the "N radio
  channels were stopped" note never showed.
- start: bot name is nested as bot.name.
- "The bot for a system" with an org-owned preferred bot now sends
  token_id (S6 accepts it today); system_id only for a platform-pinned
  pool bot, which still needs S6 to accept system_id.
- A 404 for one chosen bot no longer hides Connect and the picker
  (the message told the user to try Automatic, but the button was gone).
- Server count uses GET /tokens' per-bot server_cap when present.

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

drb-frontend/components/DiscordServersCard.tsx

@@ -28,10 +28,17 @@ const SELECT =
 
 // Option values for the bot picker: "" = let C2 choose, "tok:<id>" = one of
 // the org's own bots, "sys:<id>" = whichever bot is preferred for that system.
-function startRequest(choice: string): OAuthStartRequest {
+function startRequest(choice: string, data: OrgPreferredBots | null): OAuthStartRequest {
   const req: OAuthStartRequest = { return_to: "/settings/organization" };
   if (choice.startsWith("tok:")) req.token_id = choice.slice(4);
-  else if (choice.startsWith("sys:")) req.system_id = choice.slice(4);
+  else if (choice.startsWith("sys:")) {
+    const id = choice.slice(4);
+    // The org's own bot preferred for this system: name it by token_id, which
+    // S6 already accepts. Only a platform-pinned pool bot needs system_id.
+    const pref = data?.systems.find((s) => s.system_id === id)?.preferred_token_id;
+    if (pref) req.token_id = pref;
+    else req.system_id = id;
+  }
   return req;
 }
 
@@ -125,18 +132,19 @@ export function DiscordServersCard({ canEdit, isAdmin }: { canEdit: boolean; isA
     setActionError(null);
     setJustLinked(null);
     try {
-      const { url } = await startDiscordOAuth(startRequest(choice));
+      const { url } = await startDiscordOAuth(startRequest(choice, choices));
       window.location.assign(url);
       // Leave the button in its busy state: the page is navigating to Discord.
     } catch (err) {
       if (err instanceof OAuthNotConfigured) {
-        setOauthOff(true);
         setShowCode(true);
-        setActionError(
-          choice
-            ? "That bot can't connect servers yet. Try Automatic, or link with a code below."
-            : "Connecting with Discord isn't set up yet. Link with a code below instead.",
-        );
+        if (choice) {
+          // Only this bot is off: keep Connect and the picker so Automatic can be tried.
+          setActionError("That bot can't connect servers yet. Try Automatic, or link with a code below.");
+        } else {
+          setOauthOff(true);
+          setActionError("Connecting with Discord isn't set up yet. Link with a code below instead.");
+        }
       } else {
         setActionError(parseC2Error(err).message);
       }