Consolidate Email Settings and Automation navigation

[Proxicon]

Closes #58

Summary

• Replaces the desktop/mobile app-bar Email Settings dialog with the instance-admin-only /admin/email-settings mailbox configuration page.
• Preserves the existing HelpdeskApi GET/POST/PUT/test contract, first-record selection, masked stored-secret behavior, draft-only connection tests, explicit Save/Discard behavior, validation, dirty-navigation protection, and retryable load failures.
• Consolidates Administration navigation into Email Settings and Automation groups; removes duplicate/obsolete placements from Operations and both app-bar menus.
• Relabels the existing connectivity UI as Orchestrator while preserving /settings/connectivity and /admin/orchestration/orchestration.

Compatibility and access

• Preserved routes: /admin/pending-emails, /admin/email-rules, /admin/templates, /admin/layouts, /admin/automation, /admin/requests/services (including detail paths), /admin/ai-assistant-webhooks, /settings/connectivity, and its legacy alias.
• The new mailbox route and all relocated navigation remain HelpdeskAdmin only; tenant administration behavior is unchanged.
• No email, automation, orchestration, catalogue, or webhook engine/API behavior was expanded.

Validation

Implementation commit: fc39d4a

• dotnet restore Helpdesk.sln
• dotnet build Helpdesk.sln --configuration Release --no-restore — passed (0 errors)
• dotnet test Helpdesk.sln --configuration Release --no-build — 1146 passed, 6 existing skips, 0 failed
• npm ci
• tools/ci/run-ux-local.sh — setup 1/1 and UX 25/25 passed
• tools/ci/run-ux-local.sh tests/ux/admin-email-settings.spec.ts --output=artifacts/e2e/admin-email-settings-results — setup 1/1 and focused UX 3/3 passed
• tools/ci/check-public-disclosure.sh, tools/ci/validate-layout.sh, and the NewWeb publish bootstrap-asset smoke — passed

Synthetic desktop and mobile screenshots were captured by the local UX fixture and visually reviewed. No credentials or customer data were used.

Scope boundary

The tenant-scoped Customers/SLA follow-up noted in #57 remains separate and is not included or claimed by this PR.