chore: add community files and PSGallery publish workflow

- Add CONTRIBUTING.md, SECURITY.md, CODE_OF_CONDUCT.md
- Add .gitattributes for line ending normalization
- Add GitHub issue templates (bug report, feature request)
- Add pull request template
- Add publish.yml workflow for PSGallery publication on tag push

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/pull_request_template.md

@@ -0,0 +1,30 @@
+## Summary
+
+<!-- Brief description of the change -->
+
+## Type of Change
+
+- [ ] Bug fix
+- [ ] New feature (new cmdlet, new parameter, etc.)
+- [ ] Enhancement (improvement to existing functionality)
+- [ ] Documentation
+- [ ] CI/CD
+- [ ] Refactoring (no functional change)
+
+## Checklist
+
+- [ ] `dotnet build` succeeds with zero warnings
+- [ ] xUnit tests pass (`dotnet test`)
+- [ ] Pester tests pass (`Invoke-Pester -ExcludeTag Integration`)
+- [ ] New cmdlets added to `CmdletsToExport` in `PSProxmoxVE.psd1`
+- [ ] New cmdlets have Pester unit tests
+- [ ] `CHANGELOG.md` updated under `[Unreleased]`
+- [ ] README cmdlet reference updated (if adding new cmdlets)
+
+## PVE API Endpoints
+
+<!-- If this change adds or modifies API calls, list the endpoints -->
+
+## Testing
+
+<!-- How was this tested? Against which PVE version(s)? -->