chore: refresh dependencies and visual smoke coverage

[vipulnsward]

Summary

• Bump Ruby gems to the latest versions allowed by the existing Gemfile constraints.
• Keep Uploadcare on released Rubygems packages: uploadcare-rails 5.0.0 and uploadcare-ruby 5.0.0, constrained with ~> 5.0.
• Add a Playwright-backed visual smoke spec that covers primary pages at desktop and mobile widths.
• Document the local visual snapshot workflow and clean up file metadata form separators from the Tailwind migration.

Dependency Decisions

• pnpm: no updates available, keep as-is.
• Ruby gems: upgraded within current constraints; no Gemfile loosening needed.
• diff-lcs: bundle outdated reports 2.0.0, but rspec-expectations and rspec-mocks currently require diff-lcs < 2.0, so leave it on 1.6.2.
• Uploadcare: keep ~> 5.0 to avoid accidental major-version drift while using released 5.0.0 gems.

Verification

• bundle exec rspec — 137 examples, 0 failures
• bundle exec rubocop — 99 files inspected, no offenses
• pnpm build — passed
• git diff --check — passed
• gbrain code-check --base origin/main — score 9/10, no major blockers