Finish the Biome migration: working lint scripts, CI format check, drop dead ESLint deps

[schani]

What

Since the Biome migration in v23.2.0 (7cd667e), Biome has been this repo's formatter — but nothing ever ran it: no script, no CI, no hooks. Meanwhile the lint/lint:fix scripts still invoked ESLint, which has had no config since that same commit (and eslint itself only resolved transitively), so npm run lint has been broken for over a year. This PR finishes the migration:

• lint / lint:fix now run Biome (biome check . / biome check --write .) and pass.
• biome.json now says what we actually use: formatter on; linter and import sorting explicitly off (neither was ever adopted — Biome's default lint rules would report ~267 errors and import sorting would churn ~85 files). Adopting them is a possible follow-up, deliberately not done here.
• Ignore list fixed: test/fixtures, the vendored data/lib.d.ts, and tsconfig files are now parsed as JSONC (comments allowed), so checks measure real sources only.
• 13 drifted files reformatted (pure reflow — with no CI check, drift crept in since the original migration).
• CI now enforces formatting: a Check formatting (Biome) step in the build job (Node 20 leg; runs in well under a second).
• Biome upgraded to the current major: 1.9.4 → 2.5.3. biome migrate rewrote the config to the 2.x schema (files.ignore → negated files.includes, organizeImports → assist action) with identical intent — linter off, import sorting off, same ignore set. The 2.x formatter re-wraps 8 files (conditional-type layout in TS, multi-item array expansion in package.jsons); whitespace-only, no token changes. Four biome-ignore suppressions had the migration tool's literal <explanation> placeholder, which Biome 2 warns about — filled in with real reasons, so npm run lint is warning-free.
• Dead ESLint dependencies removed: root @typescript-eslint/eslint-plugin+parser (v6) and quicktype-vscode's eslint + @typescript-eslint/* (v7/v8) — nothing loads any of them; that package has no eslint config or lint script. Drops 76 packages from the install. Two stale eslint-disable comments removed with them.

Consequences

• Dependabot Bump @typescript-eslint/eslint-plugin from 6.21.0 to 8.63.0 #2841 (bump @typescript-eslint/eslint-plugin 6→8) becomes moot — the package no longer exists here; closing it alongside this PR.

Verification

• Fresh npm ci; npm run lint exits 0; npm run lint:fix is idempotent (no diff on second run)
• Full monorepo build; 70/70 unit tests
• quicktype-vscode still bundles (esbuild-base) without its eslint devDeps
• The exact CI step command passes locally

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