Phase 541: post-Phase-540 whiteboard implementation wave split

[ExplodingUFO]

Context

Phase 540 is tracked by GitHub #203 / avalonia-node-map-91b and PR #204. It records the readiness gate for future whiteboard persistence and render-layer work, but the roadmap still needs a concrete tracker-backed implementation wave after that gate.

AsterGraph must not jump directly from readiness wording into broad whiteboard implementation. The next step is a docs/tests-only queue split that converts the remaining whiteboard pressure into small, dependency-aware issues with clear write sets and merge ordering.

Scope

Create the post-Phase-540 implementation wave split:

• inspect the current EN/ZH React Flow parity roadmap and Phase 540 readiness criteria;
• identify the smallest next tracker-backed slices for model contract, renderer/hit-testing proof, persistence/schema policy, and Cookbook/screenshot proof;
• update EN/ZH parity docs with GitHub issue and Beads identifiers for the new wave;
• preserve stack ordering behind Phase 540 / PR Phase 540: record whiteboard persistence readiness #204;
• add focused docs tests that fail if the roadmap leaves the next whiteboard implementation wave implicit or TBD.

Out of scope

No runtime behavior changes, no public API changes, no model/schema changes, no renderer-layer changes, no screenshot manifest expansion, no Avalonia pointer coordinator edits, no UI redesign, no drawing tool implementation, no eraser behavior, no toolbar work, no retained API removal, and no full React Flow whiteboard parity claim.

Dependency / stacking

Depends on Phase 540 / PR #204. May be implemented as a stacked docs/test branch based on docs/phase-540-whiteboard-persistence-render-gate, but must not merge before Phase 540.