feat(dx): add Biome linter/formatter with lint scripts and CI step (#10)

[ayden94]

Summary

Adds Biome as the linter/formatter, replacing the .prettierrc config. Configures lint/format scripts and a CI lint step.

Changes

• Removed .prettierrc (Biome replaces Prettier)
• Added biome.json — linter enabled with recommended preset, formatter configured to match existing code style (single quotes, semicolons, trailing commas, 2-space indent, lineWidth 100)
• Updated package.json:
  • Added @biomejs/biome v2.5.5 dev dependency
  • Added lint, lint:fix, format scripts
• Updated .github/workflows/ci.yml — added pnpm lint step after typecheck, before test
• Added .changeset/biome-lint.md — patch bump

Disabled rules (conflict with existing code patterns)

Rule	Reason
useImportType	Would require changing many import lines across existing source
useHookAtTopLevel	False positives for stable callback-wrapped hooks in framework adapters
useExhaustiveDependencies	Intentional stable ref patterns in React/Solid/Vue adapters
noAssignInExpressions	Intentional ??= pattern for lazy initialization
noStaticOnlyClass	Existing pattern for namespaced static utility classes
noThisInStatic	Used in existing static utility classes
useIterableCallbackReturn	forEach with cleanup-returning callbacks is intentional
organizeImports (assist)	Would reorder existing imports across all files

noUnusedImports is set to warn (genuine issue, not blocking CI).

pnpm lint exits 0 on existing source with zero modifications required.

Verification

• pnpm lint — passes (0 errors, 1 warning)
• pnpm typecheck — passes
• pnpm test — 57/57 pass
• pnpm build — passes

Resolves #10

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