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

README.md

@@ -67,6 +67,7 @@ To install from the SD card instead, copy the `.ota` file from `.pio/build/cardp
 | `sd list` | Lists the files of each Storage Clean-up category |
 | `cat <path>` | Prints the first ~1.2 KB of a file on the SD card |
 | `irc start` | Starts the IRC Service (normally done by opening the IRC App) |
+| `irc stop` | Stops it, as `/quit` does: QUIT if connected, no more retries, and the App stays disconnected until you type |
 | `irc say <buffer> <text>` | Types into a Buffer, commands included (`irc say 0 /join #test`) |
 | `irc dump` | Prints IRC status, memory, and the last lines of each Buffer |
 | `wifi status` | Prints Wi-Fi state, network, signal, clock and free heap |