build: replace ESLint and Prettier with Biome

[AliceR]

Stacked on #69 (pnpm), which is stacked on #68 (dependency updates). Merge those first.

Replaces ESLint, Prettier and 8 plugin and config packages with Biome 2.5.14. ESLint 9 is now marked deprecated on npm, and eslint-plugin-react blocks ESLint 10, so staying on ESLint wasn't a good option.

Formatting

biome.jsonc mirrors .prettierrc (single quotes, ES5 trailing commas, semicolons, 100 cols, 2 spaces). biome format produces zero changes on the existing code.

Linting

Biome's recommended preset (roughly eslint:recommended + typescript-eslint recommended), plus the previous custom rules:

ESLint	Biome
no-console	suspicious/noConsole
react-hooks/rules-of-hooks	correctness/useHookAtTopLevel
react/self-closing-comp	style/useSelfClosingElements
react/no-array-index-key	suspicious/noArrayIndexKey
@typescript-eslint/no-explicit-any (warn)	suspicious/noExplicitAny (warn)
no-unused-vars / _ prefix	noUnusedVariables / noUnusedFunctionParameters (ignore _ by default)
@typescript-eslint/no-floating-promises, no-misused-promises	nursery/noFloatingPromises, nursery/noMisusedPromises

Verified with a probe file that each of these rules fires.

Coverage differences

• Fewer type-aware checks. Biome uses its own type inference rather than the TS compiler, so most of typescript-eslint's type-checked rules (unbound-method, restrict-template-expressions, no-base-to-string, …) have no equivalent. The promise rules are carried over, but are still in Biome's nursery group.
• useAwaitThenable is off. It reported 30 false positives on await act(async () => {}), because Biome's inference doesn't resolve React's act overloads.
• react/jsx-pascal-case has no Biome equivalent.
• Stricter: Biome's preset includes useExhaustiveDependencies, which ESLint never enabled. The one existing hit (useStacSearch.ts, reset effect) is suppressed with a reason rather than changing hook behaviour in a tooling PR.
• Example app: an override disables a11y and noShadowRestrictedNames, and allows Tailwind v3's @tailwind, so it's linted about as strictly as before; the app is due to be rebuilt.

Code changes (separate commit)

• eslint-disable → biome-ignore comments, each with a reason. react/prop-types ones were removed.
• handleStacResponse: let detail was implicitly any; now typed as GenericObject | string, matching ApiError.
• Biome's safe fixes: type-only imports where values are only used as types.
• Gotcha: Biome assumes the automatic JSX runtime by default, and its "safe" useImportType fix turned import React into import type React. That breaks tsc under our "jsx": "react". Fixed with "jsxRuntime": "reactClassic" in biome.jsonc.

Scripts and CI

• pnpm lint → biome check . (lint + format check); new pnpm format → biome format --write .
• CI lint job runs biome ci ., which emits GitHub annotations
• 8 style warnings remain (useOptionalChain in tests, noNonNullAssertion, one unused test import). Warnings don't fail CI.

Note on pnpm's minimumReleaseAge

pnpm 12 rejects versions published less than 24 hours ago. When pnpm add hits this, it silently writes a minimumReleaseAgeExclude list to pnpm-workspace.yaml. Check that file before committing after adding a dependency. Biome 2.5.15 is under 24 hours old, so this PR uses 2.5.14; #68 also holds back vite and globals for the same reason.

Verification

From a clean pnpm install --frozen-lockfile: pnpm lint and biome ci . (0 errors), pnpm test (94/94), pnpm build, and tsc --noEmit all pass.

Editor

Install the Biome VS Code extension (biomejs.biome) and set it as the default formatter instead of Prettier.

🤖 Generated with Claude Code