List the user modes in the 004 reply (closes #220)

Both transports sent an empty string as the user modes in RPL_MYINFO.
On the IRC listener that left an empty parameter in the middle of the
line, so a client that splits on spaces read the channel modes as the
user modes. The reply now lists o and w, the user modes the server
supports. Both transports read them from one constant in
internal/service, next to the code that decides which user modes MODE
accepts. The README and the schema notes now show what the HTTP API
sends.

Model: opus-5-5

internal/ircserver/conn.go

@@ -605,7 +605,7 @@ func (c *Conn) deliverWelcome() {
 	)
 	c.sendNumeric(
 		irc.RplMyInfo,
-		c.serverSfx, "neoirc", "", "mnst",
+		c.serverSfx, "neoirc", service.UserModes, "mnst",
 	)
 	c.sendNumeric(
 		irc.RplIsupport,

internal/ircserver/server_test.go

@@ -486,6 +486,22 @@ func TestWelcomeContainsNick(t *testing.T) {
 	}
 }
 
+// TestMyInfoListsUserModes checks that RPL_MYINFO lists the
+// user modes o and w, with no empty parameter before the
+// channel modes.
+func TestMyInfoListsUserModes(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+	lines := env.dial(t).register("carol")
+
+	assertContains(
+		t, lines,
+		":test.irc 004 carol test.irc neoirc ow mnst",
+		"RPL_MYINFO with user modes",
+	)
+}
+
 func TestPingPong(t *testing.T) {
 	t.Parallel()