fix(websocket): handle no-status server close

[GregHolmes]

Summary

• acknowledge a peer close so OkHttp completes the close handshake and invokes onDisconnected
• respond to Flux STT's reserved 1005 no-status sentinel with a valid 1000 close instead of throwing
• suppress reconnect only when the closing Flux Listen v2 socket accepted CloseStream; unrelated, rejected, and later-session no-status closes retain retry behavior
• add MockWebServer and listener-level regression coverage

ReconnectingWebSocketListener and the Listen v2 client remain frozen because Fern generates them; .fernignore and AGENTS.md record the patches.

Validation

• ./gradlew spotlessCheck test compileExamples
• Manual production Flux probe: after CloseStream, received one onDisconnected callback with code=1005 and observed no reconnect.

Closes #103

[GregHolmes]

Closing as superseded by #110. Fern 4.19.3 now provides the peer-close acknowledgement, valid no-status close handling, and reconnect hook; #110 retains the Listen V2 CloseStream-specific terminal policy and regression coverage.