Reduce WebSocket buffer sizes from 10MB to 64KB per connection (v0.52.12)

Previous: 10MB read + 10MB write = 20MB per connection
New: 64KB read + 64KB write = 128KB per connection

With 100 connections:
- Before: 2GB just for buffers
- After: 12.5MB for buffers

The read limit (SetReadLimit) still allows 10MB messages, but the
internal buffers don't need to be that large.

Files modified:
- app/handle-websocket.go: Reduce buffer sizes
- pkg/version/version: Bump to v0.52.12

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/handle-websocket.go

@@ -100,8 +100,10 @@ whitelist:
 	var conn *websocket.Conn
 
 	// Configure upgrader for this connection
-	upgrader.ReadBufferSize = int(DefaultMaxMessageSize)
-	upgrader.WriteBufferSize = int(DefaultMaxMessageSize)
+	// Use reasonable buffer sizes (64KB) instead of max message size (10MB)
+	// to prevent memory exhaustion with many connections
+	upgrader.ReadBufferSize = 64 * 1024  // 64KB
+	upgrader.WriteBufferSize = 64 * 1024 // 64KB
 
 	if conn, err = upgrader.Upgrade(w, r, nil); chk.E(err) {
 		log.E.F("websocket accept failed from %s: %v", remote, err)

pkg/version/version

@@ -1 +1 @@
-v0.52.11
+v0.52.12