M1 step 4a: IRC protocol core (host-tested)

lib/irc: IrcMessage parse/serialize, base64, ReconnectPolicy
(5 s .. 5 min), IrcConfig (validated, persisted) and IrcSession:
registration with SASL PLAIN or NickServ, nick fallback, PING, Buffers
capped at 50 lines with unread counts, Mentions, CTCP ACTION/VERSION,
topics, /names on request only, others' join/part/quit hidden, user
commands, and rejoining after a pause. No networking: the session
returns lines to send, Log entries and Notifications.

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

lib/irc/src/irc_message.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <initializer_list>
+#include <string>
+#include <vector>
+
+namespace roro {
+
+// One IRC protocol line: [@tags] [:prefix] COMMAND params... [:trailing] (tags are ignored).
+struct IrcMessage {
+    std::string prefix;
+    std::string command;
+    std::vector<std::string> params;
+
+    std::string nick() const { return prefix.substr(0, prefix.find('!')); }
+    std::string param(size_t i) const { return i < params.size() ? params[i] : ""; }
+
+    static IrcMessage parse(const std::string& line);
+    // Builds a line; the last parameter gets a ':' when it needs one.
+    static std::string serialize(const std::string& command, std::initializer_list<std::string> params);
+};
+
+}  // namespace roro