chore: move to mattermix/shaders

[hunterbecton]

Why

This finishes the Shaders rebrand. Package names and repo URLs already moved in the prior two commits, but user-facing prose (READMEs, AGENTS.md, the docs site, CLI strings) still called the library Matter.

What changes

npm scope rename

The published scope moves from @lovo/matter* to @mattermix/shaders*, and the internal build-only scope from @matter/* to @shaders/* (the docs, docs-tests, and editor apps, none of which publish). Every package.json, import, changeset config, and repo URL across the monorepo was updated to match.

Directory and CLI rename

packages/matter, matter-react, and matter-cli become packages/shaders, shaders-react, and shaders-cli, git-tracked as renames so history follows. MatterError becomes ShadersError in the React package's error module. The CLI's published bin moves from matter-cli to shaders-cli, and the config file it reads and writes moves from matter.config.json to shaders.config.json.

Docs site and package prose

Every README, AGENTS.md, the docs site title and wordmark, and the MDX guides now say Shaders instead of Matter. The CLI's default componentsDir moves from src/components/matter to src/components/shaders, with the docs examples, tests, and the smoke test updated to match.

Stale reference cleanup

apps/docs/content/docs/reference/matter.mdx is now shaders.mdx, since its route shouldn't carry the old brand either. The rename changed a heading's slug (@lovo/matter/color became @mattermix/shaders/color), so the color guide's anchor link needed a matching update, computed from github-slugger's rules rather than guessed.

Dead migration notes

The engine and React package READMEs both carried a "Migration from 0.3.x" section that called a set of deprecated aliases, MatterScene, MatterMonitor, MatterScheduler, and others, "still work, remove at your leisure before 0.5.0." None of those aliases exist anywhere in the current source, and the stated deadline passed several versions ago, so the sections were pure noise. Removed rather than rebranded.

Leftover identifiers

A few internal-only names survived the prior identifier pass and are now Shaders-flavored too: __MATTER_EXPORT_NAME, the shader-monitor's data-testid="matter-monitor", __matterTestReady in the visual-test harness, MATTER_E2E in the poster e2e test, and the code emitter's sortedMatter locals.

Known limitations

Two "Matter" references stay on purpose: the fake @matter-internal/lib import alias used only to test the CLI's import rewriter, and Linear's actual team name in docs/agents/issue-tracker.md, which this branch doesn't control. Package CHANGELOG.md files and .changeset/ entries keep the old brand until the follow-up PR.

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit c6edb41.}