Fix WebSocket lifecycle responsiveness

[shanselman]

Summary

• Serialize outbound WebSocket sends to prevent concurrent ClientWebSocket.SendAsync collisions.
• Thread connection cancellation from GatewayConnectionManager through GatewayClientFactory into WebSocketClientBase, with captured-socket listen loops and generation guards for stale lifecycle work.
• Move node invoke capability execution off the WebSocket receive loop using bounded observed dispatch while preserving existing response protocols.

Felt-performance/correctness risk addressed

This prevents receive loops from being blocked by long-running node capabilities, prevents fire-and-forget request sends from colliding, and avoids stale connect/reconnect work updating gateway or node state after cancellation/disconnect.

Validation

• ./build.ps1
• dotnet test ./tests/OpenClaw.Shared.Tests/OpenClaw.Shared.Tests.csproj --no-restore
• dotnet test ./tests/OpenClaw.Tray.Tests/OpenClaw.Tray.Tests.csproj --no-restore
• Additional targeted: dotnet test ./tests/OpenClaw.Connection.Tests/OpenClaw.Connection.Tests.csproj

[shanselman]

Closing this for now because it is old/dirty against the current connection stack and WebSocket lifecycle changes are high-risk to land as a drive-by during today's stability pass.

The responsiveness concern is valid, but this should come back as a fresh focused PR against current master with a targeted review and local connection lifecycle validation. Thanks for the work here; it helped identify the area that needs a cleaner follow-up.