refactor(capture): extract surface sweep record builders

[w1ne]

Summary

• extract variableSweep and surfaceFromBoundary record construction into src/modeling/capture/surfaceSweepRecords.ts
• keep CaptureSession responsible for id allocation, session lookup, OCCT endpoint evaluation, and proxy return wiring
• add direct record-shape, fallback, unresolved-metadata, and import-boundary regression coverage

Verification

• npm test -- tests/unit/capture/surfaceSweepRecords.test.ts tests/unit/capture/variableSweep.test.ts tests/unit/capture/surfaceFromBoundary.test.ts tests/unit/kernel/architectureBoundary.test.ts
• npm test -- tests/integration/variableSweepEndToEnd.test.ts tests/unit/backends/occt/variableSweepLowerer.test.ts tests/unit/capture/surfaceProxy.test.ts
• npm run typecheck
• npx eslint src/modeling/capture/captureSession.ts src/modeling/capture/surfaceSweepRecords.ts tests/unit/capture/surfaceSweepRecords.test.ts
• git diff --cached --check