IRC: join after NickServ login, keyed auto-join, SASL fallback

- With NickServ, auto-join waits for the logged-in reply (900) or 2 s
  at most, so registered-only IRC channels let us in
- A failed SASL login falls back to NickServ (its own password, or the
  SASL account and password)
- IDENTIFY names the account explicitly, and once logged in on a
  fallback nick, REGAIN takes ours back from a stale session
- Auto-join entries take keys ("#private key, #public"); keys from
  /join are reused when rejoining; keyed channels go first in JOIN
- Serial irc dump: whole Buffers, and which login is configured
  (never the secrets)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/main.cpp

@@ -193,11 +193,15 @@ static void serialCommands() {
         if (line == "irc dump") {
             Serial.printf("irc: status %d, unread %d, heap %u min %u\n", (int)irc->status(), irc->totalUnread(),
                           ESP.getFreeHeap(), ESP.getMinFreeHeap());
+            IrcConfig c = irc->draftConfig();  // which login is configured, never the secrets
+            Serial.printf("irc: nick %s, sasl %s, nickserv %s, autojoin %u channels\n", c.nick.c_str(),
+                          c.saslUser.empty() || c.saslPassword.empty() ? "off" : "on",
+                          c.nickservPassword.empty() ? "off" : "on", (unsigned)c.autojoin.size());
             irc->withSession([](IrcSession& s) {
                 for (int i = 0; i < s.bufferCount(); i++) {
                     const auto& b = s.buffer(i);
                     Serial.printf("irc buffer %d %s unread %d%s\n", i, b.name.c_str(), b.unread, b.joined ? " joined" : "");
-                    size_t from = b.lines.size() > 6 ? b.lines.size() - 6 : 0;
+                    size_t from = 0;
                     for (size_t j = from; j < b.lines.size(); j++)
                         Serial.printf("   <%s> %s\n", b.lines[j].nick.c_str(), b.lines[j].text.c_str());
                 }