Make the schema files match the server (closes #218)

Each file in schema/ now describes what the HTTP API on next sends and
accepts. A numeric reply has its name in command and its number in code.
body is always an array of strings. MODE, KICK and JOIN carry their
values in body, and TOPIC needs a non-empty body. PING takes no token,
and its PONG is the HTTP response. A channel name is limited to 63
characters, and the leading # is optional from a client.

PUBKEY.json is deleted, since the server has no such command. The
section of schema/README.md that listed the differences is removed,
and the sentences it made false are corrected.

Model: opus-5-5

schema/commands/NICK.json

@@ -2,21 +2,21 @@
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "$id": "https://sneak.berlin/go/neoirc/schema/commands/NICK.json",
   "title": "NICK",
-  "description": "Change nickname. C2S: request new nick. S2C: notification of nick change. RFC 1459 §4.1.2.",
+  "description": "Change nick. A client sends it to change its nick. The server sends it to the user's own clients and to the users who share a channel with the user. RFC 1459 §4.1.2.",
   "$ref": "../message.json",
   "properties": {
     "command": { "const": "NICK" },
-    "from": { "type": "string", "description": "Old nick (S2C)." },
+    "from": { "type": "string", "description": "The old nick. The server sets it." },
     "body": {
       "type": "array",
       "items": { "type": "string" },
-      "description": "New nick (single-element array).",
-      "minItems": 1,
-      "maxItems": 1
+      "description": "The new nick, as the first string. The server sends one string.",
+      "minItems": 1
     }
   },
   "required": ["command", "body"],
   "examples": [
+    { "command": "NICK", "body": ["newnick"] },
     { "command": "NICK", "from": "oldnick", "body": ["newnick"] }
   ]
 }