[P1] frontend: Complete ADR-007 feature route mapping

## Problem inventory
ADR-007 defines required frontend capabilities that are only partially mapped today. Some routes redirect to utility/config pages, some expected routes are absent, and one configuration component is empty.

Type: feature gap / integration regression risk

## Evidence
- docs/adr/007-frontend-modernization.md specifies /evaluation, /evaluation/[runId], and /avatar/settings.
- frontend/app/evaluation/page.tsx only redirects to /configuration/evaluation; there is no dedicated EvalDashboard or /evaluation/[runId] run viewer.
- frontend/app/avatar/settings is absent, while ADR-007 expects avatar parameter selection persisted through PUT /api/avatar/config.
- frontend/components/Configuration/Cases.tsx is an empty stub while configuration navigation exposes cases.
- frontend/README.md says the UI covers Avatar, Chat, Essays, Questions, Configuration, Upskilling, Evaluation, LMS Gateway, and APIM-routed backend traffic, so route mapping must be complete and trustworthy.

## Impact assessment
User impact: high. New functionality appears present in documentation/navigation but is not consistently reachable as mature product UI.
Blast radius: frontend routes, workspace navigation, API client integration, and service-contract expectations.

## Acceptance criteria
- [ ] Produce a route-to-capability map for all public, workspace, and configuration routes, including which backend service/API path each route depends on.
- [ ] Implement or finalize a mature /evaluation dashboard for run history, quality trends, dataset visibility, and degraded-state status.
- [ ] Implement /evaluation/[runId] for per-run details using the evaluation service contract.
- [ ] Implement /avatar/settings with voice, language, speaking style, avatar style, response length, and expertise level controls; persist with PUT /api/avatar/config when the backend route is available or define the exact backend contract if missing.
- [ ] Replace the empty cases stub with a mature cases management surface or remove the entry from navigation with documented rationale.
- [ ] Ensure every workspace navigation item resolves to a real page with role-appropriate copy and no unexpected redirect to a configuration utility page unless intentionally documented.
- [ ] Update frontend README or modernization docs with the completed route map and any deferred gaps.
- [ ] pnpm --dir frontend lint and build pass.

## Agent assignment
Primary specialist: TypeScriptDeveloper
Architecture validation: SystemArchitect
UI validation: UIDesigner

## Dependency notes
This should precede broad UI cleanup where route removal/retirement is being considered.

## Related backlog
- #123 avatar restructuring may affect the settings implementation.
- #147 avatar runtime incident is related to service readiness, not the settings UI itself.
- #143 touches frontend evaluation/history display quality.