feat: add @deck.gl-community/ai-skills — AI agent helpers for deck.gl

[charlieforward9]

Summary

This PR adds a new @deck.gl-community/ai-skills module, picking up the thread from #534 and the discussion with @ibgreen and @akre54.

The module takes the position that both approaches are correct — for different jobs — and ships them together with a single llms.txt that makes the distinction clear:

• Pattern A — native TypeScript (for LLM code generation): typed factory functions (scatterplotLayer, arcLayer, etc.) returning correct props with sensible defaults, backed by a comprehensive llms.txt reference. This directly addresses @akre54's point that "agentic coding tools work best when they can read clean documentation and write native code directly."

• Pattern B — JSON descriptors (for serializable configs and low-code UIs): fully JSON-serializable layer descriptors with dot-path accessor strings, validateDescriptor, and hydrateDescriptor. This preserves the noodle/IR approach from feat: add @deck.gl-community/visgl-skills — AI agent skills for deck.gl #534 for the cases where it genuinely shines — low-code builders, saved dashboards, server-side LLM output that can't execute code.

What's included

File	Purpose
src/layer-factories.ts	Typed factory functions for Scatterplot, Path, Polygon, Text, Arc, Heatmap
src/layer-descriptors.ts	createDescriptor / validateDescriptor / hydrateDescriptor with dot-path resolution
src/deck-builder.ts	Fluent DeckBuilder composing layers + view state into a serializable DeckConfig
src/viewport-skills.ts	fitViewport, getBoundingBox, createViewState
llms.txt	The agent reference doc — worked examples, full layer reference, decision guide for both patterns

llms.txt is included in the npm files list so it ships with the package and is accessible at node_modules/@deck.gl-community/ai-skills/llms.txt.

On the Zod direction

The validateDescriptor function is a natural slot for Zod schemas — if @ibgreen shares more on the Zod layer schema direction, it would slot in cleanly here without breaking the existing API.

Test plan

• 14 unit tests covering factories, descriptor validation, hydration, DeckBuilder, and viewport helpers
• All 57 test files in the repo pass (yarn test)
• Prettier + ESLint hooks pass

Closes #534 (supersedes the Copilot-generated PR with a more considered design)

🤖 Generated with Claude Code

[charlieforward9]

Closing in favour of #552 — this branch was accidentally based on a Copilot branch and included unrelated editable-layers changes.