fix(editor): type optional ancestor traversal for consumers

[FenjuFu]

What does this PR do?

Fixes #617. A consumer compiling the raw editor TypeScript with strict: true and noUncheckedIndexedAccess: false infers the ancestor traversal variable as AnyNode, then rejects the later undefined assignment with TS2322. Explicitly typing it as AnyNode | undefined makes the traversal compile with either setting. The added import is type-only; runtime behavior is unchanged.

How to test

1. Compile the affected ancestor traversal with TypeScript 6.0.3, strict: true, and noUncheckedIndexedAccess: false.
2. Confirm the original source reports TS2322 and this change removes it.
3. Repeat with noUncheckedIndexedAccess: true; both revisions should compile.

Local focused validation used the actual loop extracted through the TypeScript AST, structural node declarations, and the existing Record<AnyNodeId, AnyNode> scene-map contract. It reproduced the original failure and passed both configurations after the change. This is not a full workspace typecheck. git diff --check and a file-scoped Biome 2.4.16 check also passed. TypeScript 6.0.3 transpilation produced byte-identical JavaScript before and after the type-only change (12,731 bytes).

The required bun run check and bun run test commands were attempted, but the isolated checkout lacks the workspace-installed biome and turbo executables. Full workspace validation remains for CI/reviewer environment.

Screenshots / screen recording

Not applicable: this is a type-only change.

Checklist

• I've tested this locally with bun dev (not run; no runtime change)
• My code follows the existing code style (file-scoped pinned Biome passed; full bun check needs workspace dependencies)
• I've updated relevant documentation (not applicable)
• This PR targets the main branch

[pascal]

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Error id: 2ca3d529-4606-4906-8727-ef83dfb2a0e9