Prepare Esiur 3.1.0 package release and validate solution builds

CHANGELOG.md

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+# Release notes
+
+## 3.1.0
+
+- Add generation/revision cursors, resource journals, historical subscriptions,
+  and reconnect replay for live properties and events.
+- Improve dynamic resource/type definition handling and concurrent attachment
+  behavior, with cross-runtime conformance coverage.
+- Negotiate and enforce remote parser, allocation, collection, metadata-depth,
+  and encrypted-record limits.
+- Add opt-in EP connection diagnostics for traffic, queues, and resource state.
+- Standardize the default EP port at 51018 when no explicit port is supplied.
+- Update the ASP.NET Core adapter and add journal support to EntityCore.
+- Release the adapters, stores, and CLI as 3.1.0 with an Esiur 3.1.0 dependency;
+  previously published 3.0.x packages are not overwritten.
+- Correct the standalone example's endpoint display and exclude nested/stale
+  build outputs when building with an external artifacts directory.
+
+### Compatibility and publishing
+
+Use matching 3.1 runtimes when using journals, replay, or negotiated limits.
+Keep explicit endpoint ports where an installation does not use port 51018.
+Existing .NET target frameworks are unchanged.
+
+Publish `Esiur.3.1.0.nupkg` first, then `Esiur.AspNetCore`,
+`Esiur.Stores.EntityCore`, `Esiur.Stores.MongoDB`, and `Esiur.CLI` 3.1.0.
+The core security/cryptography project and test/example projects are not
+standalone NuGet products.