Remove files that should not be in repo

- Remove .claude/ settings (local Claude Code config)
- Remove CLAUDE.md files (local project instructions)
- Remove PluginCore.backup.cs (pre-refactoring backup, no longer needed)
- Remove FINDINGS.md (scratch analysis file)
- Add .claude/ and CLAUDE.md to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -366,3 +366,8 @@ FodyWeavers.xsd
 /MosswartMassacre/Unused
 /MosswartMassacre/Decal.Adapter.csproj
 /MosswartMassacre/Decal.Interop.Core.csproj
+
+# Claude Code
+.claude/
+CLAUDE.md
+**/CLAUDE.md