S7: OAuth start/options accept system_id; Discord picker QA fixes (server-26#225, #256 #257 #258)

- discord_oauth: POST /discord/oauth/start and GET /options take an optional
  system_id. The system must be the org's own or shared (another org's or
  unknown = 404). Its preferred bot is strict: one that can't connect is a
  404, never a quiet swap to Automatic. No preference = the usual order.
  The picker's "bot for a system" now always sends system_id.
- #257: _channel_state gives a bot whose token Discord rejected its own
  "invalid" state; the picker shows "Radio bot needs replacing" with no
  invite links, instead of "No radio bot".
- #256: Start no longer stays disabled on "Needs fix". It re-checks with
  Discord first (refresh=1) and starts only if the fresh answer allows it.
  "Not a voice channel" still disables Start.
- #258: own tooltip for "Not a voice channel"; "platform admin" -> "DRB
  support"; PreferredBotsCard says plainly that adding your own bot isn't
  self-serve (no support address exists yet, see #47), and a load failure
  gets a plain message + Try again instead of the raw C2 error.

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

drb-frontend/components/DiscordServersCard.tsx

@@ -28,17 +28,12 @@ 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, data: OrgPreferredBots | null): OAuthStartRequest {
+function startRequest(choice: string): OAuthStartRequest {
   const req: OAuthStartRequest = { return_to: "/settings/organization" };
   if (choice.startsWith("tok:")) req.token_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;
-  }
+  // c2-core resolves the system's preferred bot itself, including a pool bot
+  // a platform admin pinned (whose token_id the org never sees).
+  else if (choice.startsWith("sys:")) req.system_id = choice.slice(4);
   return req;
 }
 
@@ -132,7 +127,7 @@ export function DiscordServersCard({ canEdit, isAdmin }: { canEdit: boolean; isA
     setActionError(null);
     setJustLinked(null);
     try {
-      const { url } = await startDiscordOAuth(startRequest(choice, choices));
+      const { url } = await startDiscordOAuth(startRequest(choice));
       window.location.assign(url);
       // Leave the button in its busy state: the page is navigating to Discord.
     } catch (err) {