fix(web): complete bilingual workspace controls

[Tutitoos]

Related issue

Closes #190

Plan reference

Phase 8 - quality hardening and release readiness.

Summary

Completes the bilingual inbox shell so visible controls, accessible names, label disclosures, system folders, composer formatting, and thread dates follow the selected locale. Adds stable cross-platform visual regression coverage for the authenticated inbox on desktop, tablet, and mobile.

Changes

• Translate header, toolbar, mailbox, label-tree, and composer control names in English and Spanish.
• Render system mailbox names and thread dates from the active application locale.
• Exercise collapsed labels, More folders, the contextual menu, and locale changes in the inbox flow.
• Add macOS and Linux screenshot baselines for desktop-large, tablet-portrait, and mobile in both locales.

Validation

• Relevant automated checks pass

• Manual verification completed where needed

• bunx biome check --write apps/web/src/pages.tsx apps/web/tests/inbox.spec.ts

• bun run --cwd apps/web typecheck

• bun run --cwd apps/web test (50 tests)

• go test ./internal/modules/translations

• bun run --cwd apps/web build

• bun run --cwd apps/web test:e2e (30 tests across six viewport projects)

• Linux visual baselines regenerated with mcr.microsoft.com/playwright:v1.63.0-noble (3 inbox projects)

• Manually inspected English and Spanish desktop, tablet, and mobile snapshots.

Risks and rollback

The visual baselines intentionally make later layout changes explicit and may require reviewed snapshot updates. Revert commit 5e5fcc6 to restore the previous translation behavior and remove the baselines.

Checklist

• The PR has one coherent scope
• The branch and Closes reference identify the same primary issue
• The issue acceptance criteria are satisfied
• No secrets, credentials, personal data, or unintended files are included
• Documentation and tests are updated when applicable
• Breaking changes are explicitly documented (none)