feat(cli): compile page code-behind safely

[csharpfritz]

Summary

• merge the page runtime shim so \Page\ reuses \WebFormsPageBase\ and \WebFormsPage\ composes the shared head renderer
• emit compile-safe page code-behind into the generated app while quarantining pages that still contain unsupported Web Forms patterns
• add explicit BWFC global usings to scaffolded \GlobalUsings.cs\ so local project-reference migrations compile emitted .razor.cs\ files correctly
• update focused CLI tests and refresh the page/runtime docs
• capture Wingtip benchmark progression in
  un29,
  un30, and
  un31\ reports

Validation

• focused CLI tests for scaffolding, pipeline integration, and semantic pattern catalog
• fresh Wingtip migration benchmarks recorded under \dev-docs/migration-tests/wingtiptoys/run29,
  un30, and
  un31\

Wingtip impact

• run30 reduced the fresh Wingtip build from 183 errors to 60 by enabling compile-safe page code-behind emission
• run31 validated the imports fix by collapsing the deduplicated page-type import bucket (\CS0246) from 41 to 7 and exposing the next support-code/semantic failure layers