main: leftovers of the .NET 11 retarget: README runtime line, preview SDK pin, a stale remark, the smoke script's second footer #323

Problem

Four small leftovers of the .NET 11 retarget (PR #292), found by its review on 2026-10-19:

1. README.md:23 says "You need .NET 11 or later (the 10.x line stays on .NET 10)". GitHub shows this README for main, but dotnet add package CodoMetis.ValueRanges resolves 10.0.0 (net10.0) until 11.0.0 ships, and the 11 preview needs --prerelease. The README should say which version needs which runtime. The package READMEs ship inside the 11 packages, so they are right where they are read.
2. .github/workflows/release.yml:204 pins dotnet-quality: preview next to dotnet-version: 11.0.x, with no note to drop it at .NET 11 GA. The comment above it only says to bump the version with global.json.
3. The EmptyCollectionRewriter remarks on main say "Until 10.0.0 EF Core's SQL generator refused a VALUES with no rows". That was EF Core 10.0.0 and 10.0.1; 10.0.2 replaced it (EF Core 10: InvalidOperationException doing primitive list join when list is empty dotnet/efcore#37216).
4. In test/consumer-smoke-test.sh, the net11 early exit before the ComplexIndexes consumer repeats the end-of-script footer (the FAILED / passed lines). Two copies can drift apart. Cross-tests with CodoMetis.ValueRanges on both lines: range and multirange columns as temporal-constraint periods and exclusion-constraint operands EFCore.ComplexIndexes#42 removes the early exit, so this one can also just wait for that.

Change

Each one as described. No package change apart from the root README text.