Adopt the mic-check CLAUDE.md and .editorconfig house standards

Ported both files from wamplerj/mic-check and retargeted them to this project's
stack, then brought the code into line with the rules rather than watering the
rules down to fit the code.

.editorconfig — C# rules carried over verbatim, with four changes:

- Added root = true and a [*] section (utf-8, space indent, final newline,
  trim trailing whitespace). Without root the file inherits from any parent
  .editorconfig above the checkout.
- end_of_line lf rather than crlf. Every file here is LF and there is no
  .gitattributes to normalise on checkout, so crlf would rewrite the tree on
  first save.
- csharp_style_namespace_declarations file_scoped, was block_scoped. The source
  file sets file_scoped under [*.{cs,vb}] and block_scoped under [*.cs]; the
  C#-specific key wins, so the two disagreeing meant C# silently got
  block_scoped. Every .cs file here is file-scoped.
- Added sections for the React client (ts/tsx/js 2-space, 100 cols), json/yaml,
  css/html, markdown (trailing whitespace preserved — it is a line break there)
  and MSBuild files.

Also dropped a duplicated dotnet_naming_style.pascal_case block that appeared
twice verbatim in the source.

CLAUDE.md — same structure and voice, retargeted: React not Vue, xUnit and
FluentAssertions not NUnit and jest, this repo's six projects, and the real
testing approach (in-memory SQLite via TestDatabase, model calls faked at the
IAgentModelClient seam). Added sections the standards did not cover: the
three-front-ends-one-API rule, PATCH semantics, and a note that build-and-tests
green is not the same as working, with the commands to actually run each piece.

Code brought into compliance:

- Removed sealed from five types (the standard says no sealed)
- NovelAgentToolset.ExecuteAsync returned a named tuple; it now returns an
  AgentToolResult record (the standard says no tuples for return types)
- Added LangVersion latest to all six csproj files

None of the style rules produce build warnings — the IDE analyzers behind them
are off unless EnforceCodeStyleInBuild is set, and verified they stay silent
with it on too. 44 tests still pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S56bfZMGe1hnhpWP4CjjNw

tests/NovelSoftware.Tests/NovelSoftware.Tests.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <LangVersion>latest</LangVersion>
     <IsPackable>false</IsPackable>
   </PropertyGroup>