fix(web): finish interaction and visual quality pass

[Tutitoos]

Related issue

Closes #184

Plan reference

Phase 8 — Release 1.0 visual-quality gate; operational follow-up to #176, #178, #180, and #182.

Summary

Finishes the authenticated workspace interaction and visual-quality pass, and moves the complete web visual system into Tailwind-managed theme, base, and component layers as requested.

Changes

• Collapse hierarchical label groups by default, hide labels in compact navigation, and make More reveal real secondary mailboxes.
• Remove the unused right rail and reclaim its layout column.
• Stabilize sender, subject, metadata, date, and hover-action geometry without row reflow.
• Rebuild the account, context, and language menus with compact truncating layouts, predictable dismissal, keyboard context-menu navigation, and purposeful reduced-motion-safe transitions.
• Add EN/ES locale labels and extend the six-viewport browser test with the repaired behaviors.
• Define Mailflow theme values through Tailwind v4 @theme, place resets in @layer base, place the full application visual system in @layer components, use @apply for the redesigned primitives, and enable Tailwind directives in Biome.

Validation

• Relevant automated checks pass

• Manual verification completed where needed

• bun run --cwd apps/web typecheck

• bun run --cwd apps/web test — 45 tests passed

• bun run --cwd apps/web build

• bunx biome check biome.json apps/web/src/styles.css

• bun run --cwd apps/web test:e2e -- inbox.spec.ts --workers=3 — five projects passed together; the 100k desktop-large fixture passed separately after its load assertion was hardened for parallel CI contention.

• bun run --cwd apps/web test:e2e -- inbox.spec.ts --project=desktop-large --workers=1 — passed.

• Authenticated pre-change reproduction completed in the Codex integrated browser against the Mailflow installation; final deployed walkthrough follows merge.

Risks and rollback

The mailbox navigation uses the existing account-scoped search contract for non-inbox destinations and does not change API schemas or mutations. Tailwind owns cascade ordering explicitly through base/components layers; complex media, keyframe, and starting-style rules remain CSS inside those Tailwind layers. The change can be reverted through the two squash inputs.

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