Sidecar listener failure is invisible: exit 0, no stderr, error only in temp log

Split out of #110 (its observability half — the transport half is fixed by the runtime named-pipe dispatch).

When IpcConnection.CreateListener fails, SidecarHost.RunAsync logs the error to the Serilog file sink only and returns; Program.cs/Program.fs then exit 0 with nothing on stdout/stderr (sidecars/SharpLsp.Sidecar.Common/SidecarHost.cs lines 44–49). The Rust host only ever sees sidecar exited before READY (src/sidecar/manager.rs wait_for_ready), which is exactly why #110 took multiple user log uploads to diagnose. Any residual bind failure (pipe-name squat, zombie instance, ACL denial) still reproduces that opaque symptom today.

Proposed:

• Sidecar: on listener failure, write one fatal line to stderr (or FATAL:<reason> on stdout) and exit non-zero. CreateListener should also preserve exception type, not just ex.Message (IpcConnection.cs CreateListener).
• Host: when the READY wait ends in EOF, reap and report the child's exit status and include the sidecar log path (e.g. %TEMP%/sharplsp-logs/sidecar-<name>.log) in the error.

Spec refs: [DIST-FAILURE-UX], [DIST-CI-WIN-TRANSPORT].

Start with sidecars/SharpLsp.Sidecar.Common/SidecarHost.cs and IpcConnection.cs, then trace Program.cs/Program.fs and src/sidecar/manager.rs wait_for_ready. Reproduce a listener failure and observe the sidecar and host logs. Done means the sidecar reports the failure visibly with a non-zero exit, preserves the exception type, and the host reports the child status and sidecar log path.