refactor(benchmarks): isolate bitmap conformance

[thejustinwalsh]

Summary

• move finite Bitmap and source-outline wrappers from the live renderer into benchmark/targets/conformance/raster/bitmap-capture
• keep finite scene/readback/reference mechanics neutral under benchmark/low-level/raster
• rewire conformance registry, runtime fallback, and React finite-capture dispatch to the target wrapper
• enforce that no Bitmap conformance consumer imports renderer/bitmap-text
• retain the live renderer for persistent scene/font infrastructure only

Verification

• mise exec -- pnpm benchmarks:check
• 60 files / 314 unit tests
• all 19 isolated headless conformance scenarios, including exact Bitmap product and source-outline captures
• strict TypeScript, OXLint, Oxfmt, and production chunk build
• mise exec -- pnpm docs:check: 0 errors, 0 warnings

Stack

Depends on #28.