feat(ergo): a real MOTD with house rules, and honest retention wording

Replaces the placeholder MOTD with a usable one: a coloured header, five house
rules, the NickServ/ChanServ/SASL commands people actually need, and a short
"worth knowing" section.

The retention line is generated rather than hard-coded, so it matches the
deployment instead of drifting from it: HISTORY=off says messages are not
stored, otherwise it names the real HISTORY_EXPIRE. Users are told plainly that
channels are logged and for how long, which is the honest counterpart to
enabling persistent history by default.

Rendered and checked: valid UTF-8 (an invalid byte makes the whole config fail
to load), ASCII-only for old clients, no stray $-escapes, only documented colour
names, and 72 columns at the widest.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

deployments/ergo/ergo.motd

@@ -1,11 +1,27 @@
-$b__NETWORK_NAME__$r  --  __DOMAIN__
+  $c[cyan]__NETWORK_NAME__$r  --  __DOMAIN__
+  $c[cyan]============================================================$r
 
-Welcome! This network runs Ergo (https://ergo.chat).
+  Welcome! This is a small IRC network running Ergo.
 
-  Register your nick:    /msg NickServ REGISTER <password>
-  Log in on connect:     SASL PLAIN, or /msg NickServ IDENTIFY <password>
-  Register a channel:    /msg ChanServ REGISTER #channel
-  Help:                  /msg NickServ HELP  and  /msg ChanServ HELP
+  $bHouse rules$r
+    1. Be decent to one another. No harassment, hate speech, or
+       personal attacks.
+    2. No spam, flooding, or unsolicited advertising.
+    3. Keep it legal, and roughly work-safe unless a channel's
+       topic says otherwise.
+    4. Don't evade bans. If you disagree with an operator, take it
+       to a private message rather than into the channel.
+    5. Channels may add rules of their own -- read the /TOPIC.
 
-Be kind to each other. Operators are listed in /ADMIN.
-(Edit this file with: ergoctl motd)
+  $bGetting set up$r
+    Register your nick    /msg NickServ REGISTER <password>
+    Stay logged in        enable SASL PLAIN in your client
+    Register a channel    /msg ChanServ REGISTER #channel
+    Help                  /msg NickServ HELP   /msg ChanServ HELP
+
+  $bWorth knowing$r
+    __HISTORY_NOTE__
+    Your IP address is hidden from other users, but not from staff.
+    Questions or appeals: message an operator -- see /ADMIN.
+
+  Enjoy your stay.