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/update_service.h

@@ -35,7 +35,6 @@ class UpdateService : public Service {
     int percent() const { return percent_; }
     std::string incomingVersion() const;
     bool onProbation() const { return probation_; }
-    const std::string& hostname() const { return hostname_; }
 
     // Installs an Update File from the SD card (runs on the storage task).
     void installFromSd(const std::string& path);
@@ -58,7 +57,6 @@ class UpdateService : public Service {
     EventBus& bus_;
     const Settings& settings_;
     TaskHandle_t task_ = nullptr;
-    std::string hostname_;
     volatile Phase phase_ = Phase::Idle;
     volatile int percent_ = 0;
     std::string incoming_;