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

lib/irc/src/irc_config.h

@@ -7,6 +7,11 @@
 
 namespace roro {
 
+struct IrcChannel {
+    std::string channel;  // "#roro"
+    std::string key;      // empty when the IRC channel has none
+};
+
 // The one IRC server the IRC Service connects to, persisted in internal flash.
 class IrcConfig {
    public:
@@ -20,7 +25,7 @@ class IrcConfig {
     std::string nick;
     std::string saslUser, saslPassword;  // SASL PLAIN when both are set
     std::string nickservPassword;        // otherwise IDENTIFY with NickServ, if set
-    std::vector<std::string> autojoin;
+    std::vector<IrcChannel> autojoin;
 
     // A copy is a draft the UI can edit freely; copySettingsFrom() applies one.
     IrcConfig(const IrcConfig&) = default;
@@ -41,8 +46,10 @@ class IrcConfig {
     std::string save();  // empty on success, otherwise why it was refused
     std::string validate() const;
 
-    static std::vector<std::string> parseChannels(const std::string& text);
-    static std::string formatChannels(const std::vector<std::string>& channels);
+    // "#private key, #public": a word starting with # or & is an IRC channel, the word after it
+    // (if it doesn't) its key. Spaces or commas separate entries, so "#a #b" also reads.
+    static std::vector<IrcChannel> parseChannels(const std::string& text);
+    static std::string formatChannels(const std::vector<IrcChannel>& channels);
 
    private:
     KeyValueStore& store_;