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

schema/README.md

@@ -144,8 +144,8 @@ Where a schema file and the HTTP API disagree, the HTTP API is right:
   with `ERR_NEEDMOREPARAMS` (`461`). A `body` of `[""]` clears the topic.
 - `003.json` describes the server's creation date. The HTTP API sends the date
   the server last started.
-- `004.json` has example mode lists. The HTTP API sends an empty string as the
-  user modes and `ikmnostl` as the channel modes.
+- `004.json` has example mode lists. The HTTP API sends `ow` as the user modes
+  and `ikmnostl` as the channel modes.
 - `322.json` says `LIST` gets one reply per channel. The server leaves out a
   secret channel, one with mode `+s`, unless the user is on it.
 - `332.json` says `RPL_TOPIC` answers a `TOPIC` query. The HTTP API has no such