fix(cadente): rebuild listener on fatal accept errors

[CypherPotato]

Motivation

• The listener can become permanently invalid after a network interface reset (observed on Android) and the accept loop keeps retrying the same broken socket instead of recovering.
• Synchronous AcceptAsync failures (and unexpected ObjectDisposedException) should be treated like fatal async accept errors so the listener can be rebuilt.

Description

• Treat synchronous accept failures by inspecting SocketException.SocketErrorCode in StartAccept and trigger the same listener rebuild path used for fatal accept completions via TriggerListenerRebuild when appropriate.
• Add a recovery path for ObjectDisposedException during AcceptAsync that triggers a rebuild while the host is still listening and not already restarting.
• Harden TriggerListenerRebuild so it no-ops when the host is stopped or disposed and keep the single-flight rebuild guard using _listenerRestarting.
• Implement RebuildListenerAsync to dispose the old listener, create a replacement listener with retry delays, dispose partially-created replacement sockets on failure, and restart all accept slots when rebuild succeeds.

Testing

• git diff --check ran with no reported whitespace/errors.
• dotnet build cadente/Sisk.Cadente/Sisk.Cadente.csproj -c Release succeeded and produced build artifacts and NuGet packages (build emitted SourceLink warnings because the repository has no remote).

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Codex Task