fix(ci): ignore generated pnpm lockfile

[XxKotfeJxX]

What changed

• excluded pnpm-lock.yaml from frontend Prettier checks
• preserved existing ignores for build output, coverage, and dependencies

Why

Dependabot regenerates pnpm-lock.yaml when updating frontend dependencies. Prettier reformats that generated lockfile, so otherwise valid dependency pull requests failed at pnpm format:check before typecheck, tests, and build could run.

Impact

Source files remain formatting-gated, while the pnpm-owned lockfile is validated by pnpm install --frozen-lockfile instead of Prettier. This allows Dependabot PRs targeting dev to run their meaningful CI checks.

Validation

• pnpm --dir web format:check
• git diff --check
• Prettier check against the regenerated lockfile from Dependabot PR chore(deps-dev): bump typescript from 5.9.3 to 6.0.3 in /web #6