Add embedded web chat client (closes #7) (#8)

schema/commands/JOIN.json

@@ -0,0 +1,16 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://git.eeqj.de/sneak/chat/schema/commands/JOIN.json",
+  "title": "JOIN",
+  "description": "Join a channel. C2S: request to join. S2C: notification that a user joined. RFC 1459 §4.2.1.",
+  "$ref": "../message.json",
+  "properties": {
+    "command": { "const": "JOIN" },
+    "from": { "type": "string", "description": "Nick that joined (S2C)." },
+    "to": { "type": "string", "description": "Channel name.", "pattern": "^#[a-zA-Z0-9_-]+$" }
+  },
+  "required": ["command", "to"],
+  "examples": [
+    { "command": "JOIN", "from": "alice", "to": "#general" }
+  ]
+}