v1.1.0 — Gzip canvas compression + throttled sends

- Canvas snapshots gzip-compressed before sending: 1MB raw -> ~1-5KB
  for a mostly-white canvas, ~100-500KB for a busy one
- Semaphore throttles concurrent canvas sends (default 20) to prevent
  memory spikes during connection bursts
- Frontend decompresses gzip via browser DecompressionStream API
- New config: MAX_CONCURRENT_CANVAS_SENDS (default 20)
- Added flate2 dependency for gzip encoding

crates/adapters/websocket/Cargo.toml

@@ -7,6 +7,7 @@ edition.workspace = true
 application = { workspace = true }
 domain = { workspace = true }
 axum = { workspace = true, features = ["ws"] }
+flate2 = { workspace = true }
 futures = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }