Add RenderInfo with lazy element bounds lookup

[cowboyd]

Motivation

Higher-level frameworks need access to computed element bounding boxes after layout — for scroll containers, floating tooltips, or dirty-region tracking. Element IDs are now stable (hashed with seed 0), so callers can look up any element by id after rendering.

Approach

Adds a single WASM export get_element_bounds(name, len, out) that hashes the id string, calls Clay_GetElementData(), and writes the bounding box to a float buffer. No tables, no globals — one function handles the lookup.

On the TypeScript side, RenderResult gains an info: RenderInfo field with a lazy get(id) method that calls into WASM on demand:

interface RenderInfo {
  get(id: string): ElementInfo | undefined;
}

interface ElementInfo {
  bounds: BoundingBox;
}

interface BoundingBox {
  x: number;
  y: number;
  width: number;
  height: number;
}

Querying an unknown or empty-string id returns undefined.

Alternate Designs

Earlier iterations materialized the full map eagerly using global tables and seven accessor functions. The lazy approach is simpler — one WASM export, no state, callers only pay for what they query.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/clayterm@22

commit: a9eec48