build(deps): bump @biomejs/biome to 2.5.3

[mindsers]

Summary

• Bumps @biomejs/biome from 2.4.16 to 2.5.3 (the piece that was carved out of build(deps): bump the patch-and-minor group with 23 updates #270 / build(deps): bump the patch-and-minor group across 1 directory with 22 updates #272 via @dependabot ignore).
• Biome 2.5.3 promotes two rules to hard errors, exposing six pre-existing spots:
  • lint/correctness/noUnsafeOptionalChaining in three test files where mock-call args were cast with x?.y as T and then dereferenced. Reworked as const [call] = mock.calls[0] plus a single cast, so the type asserts the presence Biome now requires without adding runtime checks.
  • lint/a11y/noSvgWithoutTitle in public/icon.svg — added a <title>Unitae</title> element.
• The remaining ~60 diagnostics from Biome 2.5.3 (nursery/useSortedClasses, complexity, useAwait, unused imports) are warnings/infos already present on main and don't block CI. Left them for a follow-up.

Once this merges, Biome will still be pinned in Dependabot config from the earlier @dependabot ignore @biomejs/biome minor version on #270 — no action needed unless we want future minor bumps proposed automatically, in which case comment @dependabot unignore @biomejs/biome on any Dependabot PR.

Test plan

• `pnpm test:lint` — clean (0 errors, warnings baseline unchanged)
• `pnpm test:typecheck` — clean
• `pnpm test:unit` — 2205/2205 pass
• Full CI on the PR