Inline placement helpers into transform and remove api/placement.js

[tracygardner]

Motivation

• Review feedback removed the need for a separate placement module, so keep the migration seam local to api/transform.js to avoid expanding the public API surface prematurely.
• Preserve existing placement semantics while making a small, reversible change that makes further migration easier.

Description

• Deleted api/placement.js and removed its flock wiring from flock.js (import, spread, and initialization call) to avoid unused API surface.
• Added local helpers resolvePositionInputs and applyPositionWithCurrentBaseRule inside api/transform.js and updated positionAt to call applyPositionWithCurrentBaseRule instead of inlining the base-alignment logic.
• Kept runtime behavior intact by preserving the base-alignment rule (requested Y maps to mesh base/minimumWorld.y) while centralizing the logic inside api/transform.js for incremental migration.

Testing

• Ran npm run lint, which failed due to existing unrelated lint issues in flock.js (two no-empty block statements and an undefined hideLoadingScreen), so lint did not pass; the failures are pre-existing and outside the change scope.
• Committed the changes locally with message Inline placement scaffold in transform and remove extra placement module and updated the PR description to reflect the review-driven removal of the extra module.

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Codex Task