chore: drop ESLint in favor of Biome

[kyscott18]

Consolidates linting on Biome and removes ESLint.

Rationale

• Next 16 removed the built-in ESLint integration (next lint + lint-at-build). ESLint here was opt-in and not wired into CI or the build, so eslint-config-next's @next/next rules weren't actually enforced.
• Biome (already the CI lint job via biome ci) covers linting + formatting + import organization, plus rules-of-hooks and a large chunk of jsx-a11y.
• No regression vs. what's enforced today. Tradeoff: the Next-specific @next/next rules (no Biome equivalent) are no longer available — but they weren't enforced before this change either.

Changes

• Remove the "lint": "eslint" script and the eslint / eslint-config-next devDependencies from frontend/package.json.
• Delete frontend/eslint.config.mjs.
• Drop "eslint.enable" from .vscode/settings.json (Biome is the formatter/linter).
• Update root pnpm-lock.yaml (removes eslint + ~300 transitive deps).

Verification (pnpm 10, Node 22, locally)

• pnpm install --frozen-lockfile ✓
• pnpm typecheck ✓
• biome ci ✓ (only the pre-existing noNonNullAssertion warning)

Stacked on #103 (linear: #100 → #101 → #103 → this). Retarget base to main once the lower PRs merge.

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Project	Deployment	Actions	Updated (UTC)
monode	Ready	Preview, Comment	Jun 9, 2026 8:00pm

[greptile-apps]

Greptile Summary

This PR removes ESLint from the frontend package and fully consolidates on Biome, which was already the enforced linter in CI (biome ci) and the default formatter in the VS Code workspace config. The root package.json already exposes "lint": "biome check ." as the canonical lint entry point, so no developer workflow is broken.

• Deletes frontend/eslint.config.mjs, removes eslint/eslint-config-next devDependencies and the "lint": "eslint" script from frontend/package.json, and strips eslint.enable from .vscode/settings.json.
• Updates pnpm-lock.yaml to drop ~300 ESLint transitive dependencies; the Biome biome.json (with recommended rules, rules-of-hooks coverage, and jsx-a11y subset) remains the single source of lint truth.

Confidence Score: 5/5

Safe to merge — purely removes ESLint tooling that was never wired into CI or the build, with Biome already covering the linting path end-to-end.

All changed files are tooling/config only: deleted ESLint config, removed devDependencies, dropped an unused VS Code setting, and updated the lockfile. Biome is already the enforced linter in CI and the root workspace lint script remains intact. No application logic, tests, or runtime behaviour is touched.

No files require special attention.

Important Files Changed

Filename	Overview
frontend/package.json	Removes the lint script and eslint/eslint-config-next devDependencies; linting is now delegated to the root biome check . script and CI biome ci job.
frontend/eslint.config.mjs	Deleted ESLint flat-config file that extended eslint-config-next/core-web-vitals and eslint-config-next/typescript; no longer needed once Biome is the sole linter.
.vscode/settings.json	Drops eslint.enable: true; Biome VS Code extension is already configured as the default formatter and linter for all relevant file types.
pnpm-lock.yaml	Lockfile update removing ~300 ESLint transitive dependencies from the workspace; generated change consistent with the package.json edits.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    subgraph Before["Before this PR"]
        A[Developer saves file] --> B[ESLint VS Code extension]
        A --> C[Biome VS Code extension]
        D[CI lint job] --> E["biome ci (enforced)"]
        F["pnpm lint (frontend)"] --> G["eslint (not in CI)"]
    end

    subgraph After["After this PR"]
        H[Developer saves file] --> I[Biome VS Code extension]
        J[CI lint job] --> K["biome ci (enforced)"]
        L["pnpm lint (root)"] --> M["biome check ."]
    end

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