chore(claude): improve Claude Code integration

.claude/commands/precommit.md

@@ -0,0 +1,8 @@
+Run the pre-commit checklist for this project:
+
+1. Remind me to update `CHANGELOG.md` `[Unreleased]` section (Added / Changed / Fixed / Removed) — I must do this manually.
+2. Run `dotnet build --configuration Release` — must succeed.
+3. Run `dotnet test --settings .runsettings` — all tests must pass.
+4. Run `dotnet csharpier --check .` — must pass (run `dotnet csharpier .` to auto-fix).
+
+Run steps 2–4, report the results clearly, then propose a branch name and commit message for my approval using the format `type(scope): description (#issue)` (max 80 chars; types: `feat` `fix` `chore` `docs` `test` `refactor` `ci` `perf`). Do not create the branch or commit until I explicitly confirm.

.claude/settings.json

@@ -1,3 +1,7 @@
 {
-  "model": "claude-sonnet-4-6"
+  "permissions": {
+    "allow": [
+      "Bash(dotnet *)"
+    ]
+  }
 }

.vscode/extensions.json

@@ -4,7 +4,7 @@
     "ms-dotnettools.csdevkit",           // C# Dev Kit - Official Microsoft C# tooling
 
     // AI Assistance
-    "github.copilot-chat",               // GitHub Copilot Chat - AI-powered coding assistant
+    "anthropic.claude-code",             // Claude Code - AI-powered coding assistant
     "coderabbit.coderabbit-vscode",      // CodeRabbit - AI-powered code review
 
     // Code Quality

CLAUDE.md

@@ -1,3 +1,7 @@
 # CLAUDE.md
 
 @.github/copilot-instructions.md
+
+## Claude Code
+
+- Run `/precommit` to execute the full pre-commit checklist for this project.