Phase 563: whiteboard annotation screenshot and Cookbook proof expansion

[ExplodingUFO]

Summary

• Adds the Phase 563 docs/tests planning gate for WHITEBOARD_ANNOTATION_SCREENSHOT_COOKBOOK_PROOF_EXPANSION.
• Defines Cookbook route expectations, screenshot proof metadata, non-overlap requirements, and separation from persistence/serialization implementation.
• Keeps the slice docs/tests-only: no screenshot manifest expansion, no new Cookbook route, no UI behavior change, no persistence/serialization/schema/public API/saved-state/full parity claim.

Verification

• RED: dotnet test tests\AsterGraph.Demo.Tests\AsterGraph.Demo.Tests.csproj --filter "FullyQualifiedName~ReactFlowParityRoadmapDocsTests.ParityRoadmapDocs_RecordPhase563ScreenshotCookbookProofExpansionInBothLocales" failed before docs update on missing marker WHITEBOARD_ANNOTATION_SCREENSHOT_COOKBOOK_PROOF_EXPANSION.
• GREEN focused: same command passed 1/1 after docs update.
• dotnet test tests\AsterGraph.Demo.Tests\AsterGraph.Demo.Tests.csproj --filter "FullyQualifiedName~ReactFlowParityRoadmapDocsTests" passed 63/63.
• git diff --check exited 0 with only LF-to-CRLF warnings.
• dotnet build AsterGraph.sln -c Release succeeded with 0 warnings/errors.
• dotnet test AsterGraph.sln passed Demo.Tests 308/308 and Editor.Tests 887/887.
• dotnet test tests\AsterGraph.Demo.Tests\AsterGraph.Demo.Tests.csproj passed 308/308.

Stacked after PR #250 / Phase 562. Do not merge before lower stack lands.

[ExplodingUFO]

Phase 563 final stacked handoff after restack:

• Restacked base: 07248c37579cc21c3574ef396729f49a2872681b (PR Phase 562: annotation clipboard/export boundary #250 / Phase 562 head)
• Restacked head: 614d07817fa4330d6303753d2bbc778f07082432
• Range-diff check: git range-diff 20d2272..backup/phase-563-before-restack-20260514 07248c3..HEAD shows the single Phase 563 commit as equivalent after replay.
• Local verification:
  • ReactFlowParityRoadmapDocsTests: 63/63 passed
  • Release build: 0 warnings / 0 errors
  • AsterGraph.Demo.Tests: 308/308 passed
  • git diff --check: clean
• Remote verification: PR is MERGEABLE / CLEAN at this head.
• CI: all duplicate status checks passed, including hygiene-proof, framework-matrix net8.0/net9.0/net10.0, linux-validation, macos-validation, contract-proof, and both release-validation jobs.

Still intentionally blocked only by stack order behind PR #250 and lower stack PRs.