Harden code quality: shared Biome config + CI gate

[kualta]

Adopts the shared @flow-industries/lint Biome preset and adds a lint + typecheck CI gate. Second repo in the cross-repo hardening rollout (after flow-industries/docs#29).

What changed

• biome.json — extends @flow-industries/lint/biome + /react; ignores CSS (Biome can't parse Tailwind v4 directives).
• package.json — adds lint / format / check / typecheck scripts; pins @biomejs/biome@2.4.12; adds @flow-industries/lint.
• .github/workflows/ci.yml — new; calls the reusable ts-check.yml@v1 workflow (lint + tsc --noEmit) on pushes and PRs.
• a11y fixes in published components (first lint pass ever on this repo):
  • type="button" on the animated-icons copy button (prevents accidental form submits)
  • brand icon SVGs (X, Discord, GitHub, Bluesky) get role="img" + <title>; the accordion chevron is marked aria-hidden
  • removed a redundant role="navigation" on <nav> (pagination)
  • removed an unnecessary hook dependency in sidebar; == → === in field; stable keys for field error lists
• Deliberate patterns kept, with scoped biome-ignore + reason: shadcn/Base-UI role attributes on styled divs (button-group, field, input-group, item, carousel, breadcrumb, OTP separator), the chart <style dangerouslySetInnerHTML> (static CSS from config), and positional index keys (slider thumbs, recharts payloads). Changing those DOM elements would alter published component rendering — out of scope for a lint PR.

Note on the diff

The first commit is pure mechanical formatting (57 files); the second has the wiring + semantic fixes (20 files). 8 style-level warnings remain (non-null assertions, document.cookie) — they don't fail CI and can be burned down separately.

Verified locally: bun run lint, bun run typecheck, and bun run build all pass.