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/NodeDiscordRadio.tsx

@@ -116,8 +116,8 @@ function DiscordPicker({
   const channelOnHere = channel?.stream?.node_id === nodeId;
   const check = guildId ? checks[guildId] : undefined;
   const checkOn = check?.data?.enabled !== false;
-  const verdictOf = (c: DiscordGuildOption["voice_channels"][number]) => {
-    const row = check?.data && checkOn ? check.data.channels[c.channel_id] : undefined;
+  const verdictOf = (c: DiscordGuildOption["voice_channels"][number], data: VoiceCheck | null | undefined = check?.data) => {
+    const row = data && data.enabled !== false ? data.channels[c.channel_id] : undefined;
     const v = channelVerdict(row);
     // This system already plays here: c2-core counts its bot as busy (it holds
     // the channel), so the channel can read "Needs fix"/"Bots busy" for a NEW
@@ -128,19 +128,26 @@ function DiscordPicker({
   };
   const chosenVerdict = channel ? verdictOf(channel) : null;
   const definiteDeny = blocksStart(chosenVerdict);
+  // "Not a voice channel" can't change, so Start stays off. "Needs fix" can:
+  // Start re-checks with Discord first (server-26#256), so fixing it in
+  // Discord and pressing Start again just works — no hunting for Re-check.
+  const startOff = chosenVerdict?.kind === "not_voice";
+  // Not for "invalid": that bot is already in the server; inviting won't help (#257).
   const showInvite = chosenVerdict?.kind === "fix" || chosenVerdict?.kind === "no_bot" || chosenVerdict?.kind === "busy";
 
   const runCheck = useCallback(
-    async (gid: string, refresh: boolean) => {
+    async (gid: string, refresh: boolean): Promise<VoiceCheck | null> => {
       setChecks((m) => ({ ...m, [gid]: { data: m[gid]?.data ?? null, busy: true, error: null, limited: false } }));
       try {
         const data = normalizeVoiceCheck(await c2api.getNodeVoiceCheck(nodeId, gid, refresh));
         setChecks((m) => ({ ...m, [gid]: { data, busy: false, error: null, limited: refresh && data.refreshed === false } }));
+        return data;
       } catch (err) {
         const e = parseC2Error(err);
         // 404 = route not deployed yet or server not visible: no badges (fail-open).
         const msg = e.status === 404 ? null : e.message;
         setChecks((m) => ({ ...m, [gid]: { data: m[gid]?.data ?? null, busy: false, error: msg, limited: false } }));
+        return null;
       }
     },
     [nodeId],
@@ -166,6 +173,12 @@ function DiscordPicker({
     setSending(true);
     setError(null);
     try {
+      if (definiteDeny) {
+        // Fresh answer from Discord; still refused = stay here, the row shows why.
+        // A failed check fails open, like everywhere else in the picker.
+        const fresh = await runCheck(guild.guild_id, true);
+        if (fresh && blocksStart(verdictOf(channel, fresh))) return;
+      }
       await c2api.startNodeDiscordStream(nodeId, { guild_id: guild.guild_id, channel_id: channel.channel_id, mode });
       onStarted();
       onClose();
@@ -382,11 +395,17 @@ function DiscordPicker({
           <button
             type="button"
             onClick={start}
-            disabled={sending || !channel || !options.system_id || (atNodeCap && !channelOnHere) || definiteDeny}
-            title={definiteDeny ? "No radio bot in this server can stream into this channel — fix the permission in Discord, then Re-check." : undefined}
+            disabled={sending || !channel || !options.system_id || (atNodeCap && !channelOnHere) || startOff}
+            title={
+              startOff
+                ? "That is not a voice channel. Pick a voice channel."
+                : definiteDeny
+                  ? "Fixed the permission in Discord? Start checks again first."
+                  : undefined
+            }
             className="flex-1 bg-accent hover:brightness-110 disabled:opacity-50 disabled:cursor-not-allowed text-white rounded-lg py-2 text-sm font-semibold"
           >
-            {sending ? "Starting…" : channelOnHere ? "Update" : "Start radio"}
+            {sending ? (definiteDeny ? "Checking…" : "Starting…") : channelOnHere ? "Update" : "Start radio"}
           </button>
           <button
             type="button"