MSBuildInstanceSelector: exact Roslyn version equality — SDK servicing skew falls back to a known-broken registration

From the multi-agent audit (sidecars/SharpLsp.Sidecar.CSharp/MSBuildInstanceSelector.cs ~166): SDK selection accepts an SDK only when its Roslyn assembly version EXACTLY equals the bundled one; any servicing skew (e.g. bundled 5.6.0.0 vs SDK 5.6.1.0) rejects every SDK and falls back to a registration already known not to satisfy the bundled surface — reproducing the #159 crash-loop class on machines that are actually fine.

Selection should accept any SDK whose Roslyn is >= the bundled surface's requirement (or better: stop depending on the SDK's Roslyn at all now that #159 ships the full bundled set — verify which assemblies still resolve from the MSBuild directory and pin/carry them).

Relates: #135, #159.

Read sidecars/SharpLsp.Sidecar.CSharp/MSBuildInstanceSelector.cs around line 166 and compare the exact Roslyn-version check with the bundled assembly behavior from #159. Verify which assemblies still resolve from the MSBuild directory and whether servicing versions can be accepted without falling back to the known-broken registration. Done means SDK selection avoids the #159 crash-loop case on machines with a servicing skew.