Tooling drift: dual mathjs sources, no lint/format, smoke needs global Playwright

[zntznt]

Problem

Tooling drift across the repo: no lint/format/coverage config, two sources of truth for mathjs, and the smoke suite depends on a global install.

Evidence

• No lint, format, or coverage config in the repo (an eslint-disable comment hints at ad-hoc use only).
• Two math.js sources must be kept in sync by hand: the vendored bundle (vendor/math.js) vs the npm mathjs the tests use.
• test/smoke.js requires Playwright from a global NODE_PATH — friction for fresh clones.
• Root-level audit2.js / audit_screenshots.js are undocumented one-off scripts with hardcoded paths, not in CI or the README file table.
• No test filter flag, so running one test means running the whole suite.

Expected

• A minimal lint/format config (or an explicit decision to have none, documented).
• A single mathjs source (or a sync check in CI).
• Smoke/audit tooling documented or removed.

Impact

Each of these is small, but together they make the toolchain the least trustworthy part of an otherwise disciplined repo.