feat: add option to disable pixel placement

polylan_submitter/place/wire.py

@@ -6,8 +6,10 @@ either). Each message is a short string: a one-letter type tag followed by
 '|'-separated fields, in a fixed order the client already knows from this
 table:
 
-    s|<next>|<width>|<height>    initial personal state, once per connection
-                           (next = epoch ms cooldown ends, or empty if free now)
+    s|<next>|<width>|<height>|<on>
+                           initial personal state, once per connection
+                           (next = epoch ms cooldown ends, or empty if free now;
+                           on = 1 if placing pixels is allowed, 0 if frozen)
     p|<x>|<y>|<c>          a pixel was placed - broadcast to everyone,
                            including the placer (no separate ack needed)
     k|<next>               your own placement was accepted; carries your
@@ -15,10 +17,13 @@ table:
     r|c|<next>             rejected: still on cooldown
     r|a                    rejected: not logged in
     r|i                    rejected: invalid x/y/color
-    e|<width>|<height>     an admin resized the grid for this event -
-                           broadcast to everyone. A client that sees this
-                           should re-fetch /api/.../place/canvas rather than
-                           try to remap its local pixels.
+    r|d                    rejected: placement is disabled by an admin
+    e|<width>|<height>|<on>
+                           an admin edited this event's settings (grid size
+                           and/or placement toggle) - broadcast to everyone.
+                           If the size changed, a client should re-fetch
+                           /api/.../place/canvas rather than try to remap its
+                           local pixels.
 
 Client -> server has exactly one message shape, the same as the broadcast:
 p|<x>|<y>|<c>