docs: add CONTEXT.md — a codebase glossary

[bigmistqke]

Summary

Adds a root CONTEXT.md — a domain glossary for solid-three — establishing the canonical vocabulary for the codebase and recording the ambiguities/renames we've resolved. Also untracks docs/superpowers/ (local process artifacts that were committed in #62 despite being gitignored; files kept locally).

What's in CONTEXT.md

• Element model — element (any managed three.js value) vs object (an Object3D) vs instance (pre-built, via from).
• Declaring / configuring — entity (element-component), catalogue, T namespace; args, attach, dashed path.
• Runtime — Canvas, Context, renderer (the concept behind gl), frame callback.
• Plugins — Plugin, selector, plugin prop (+ override), Register.
• Events & pointers — event.object / currentObject, intersection, raycast vs tree propagation, pointer source / Pointer / raycaster / NDC, pointer capture / drag plane / hasPointerCapture.
• Components & lifecycle — Portal, Resource, Viewport, disposal, XR.
• Plus Relationships, an example dialogue, and flagged ambiguities documenting each rename.

Decisions recorded for later cleanup PRs

• gl → renderer — gl is a misnomer once WebGPURenderer is supported; rename the Canvas prop + Context field later (keep gl as a deprecated alias for a release).
• "contributed method" → plugin prop — rename the concept and code (resolvePluginMethods, etc.).

Notes

• Docs-only; no runtime change (the only code-adjacent change is untracking docs/superpowers).
• The bubble() → propagate() rename shipped in feat(events)!: pointer capture + reactive hasPointerCapture + object/currentObject event API #69 already follows this glossary.

[pkg-pr-new]

• solid-three-demo

  npm i https://pkg.pr.new/solid-three@71
  

commit: 03d940c

[bigmistqke]

Folded into #63 — the CONTEXT.md glossary now ships there alongside the git-workflow docs (one "docs & process" change, one docs/superpowers untrack). Closing.