Stop IRC by hand; remove mDNS

IrcService::disconnect() stops the session from any state: QUIT if
connected, then no more retries. /quit goes through it (before, it only
stopped a connected session; while waiting for Wi-Fi or retrying it did
nothing), and so does the new `irc stop` command. Stopped by hand,
opening the IRC App no longer reconnects; typing a line does.

mDNS is gone: it never crossed the dev box's routed network, and it
cost about 7.5 KB of RAM. Pushes go to the IP shown in Settings ->
Firmware, which drops its Name row. OTA Q54 records the change.

On the device, Debug Build: 105.6 KB free with Wi-Fi (was 98); with IRC
on TLS 54 KB free (was 46); after `irc stop`, back to 99 KB.

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

src/services/irc_service.h

@@ -31,9 +31,12 @@ class IrcService : public Service {
     const char* name() const override { return "irc"; }
     void start() override;
 
-    // Starts the session (the IRC App does this when opened); /quit stops it.
+    // Starts the session (the IRC App does this when opened, unless you stopped it).
     void connect();
+    // Stops it, from any state: says QUIT if connected, and stops retrying. /quit, `irc stop`.
+    void disconnect();
     bool running() const { return wanted_; }
+    bool stoppedByUser() const { return stoppedByUser_; }
     Status status() const { return status_; }
 
     // Read or act on the session while holding its lock: withSession([](IrcSession& s) { ... }).
@@ -78,6 +81,9 @@ class IrcService : public Service {
     ReconnectPolicy backoff_;
     std::string partial_;
     volatile bool wanted_ = false;
+    volatile bool stoppedByUser_ = false;  // a manual stop: opening the App doesn't reconnect
+    volatile bool stopRequested_ = false;
+    bool quitSent_ = false;  // /quit already queued its QUIT
     volatile bool restart_ = false;
     volatile Status status_ = Status::Stopped;
     bool open_ = false;