feat(phase-7-frontend): anomaly feed UI + nav badge + Settings toggle (+31 bUnit tests)

Frontend portion of Phase 7. Backend (commit a6ff368) had already shipped
the AnomalyDetector, DetectAnomaliesUseCase, AnomalyDetectionPoller, and
all DI wiring. This commit adds the user-facing surfaces.

New surfaces (Option A routing — folder-per-feature):
- Pages/Anomalies/AnomalyFeed.razor (@page /anomalies) — replaces the
  Phase 5 placeholder with a severity-coded card stream, filter chips
  (severity / sport / date), unread-count summary, 'Mark all read' action.
- Pages/Anomalies/Detail.razor (@page /anomalies/{id:guid}) — m-detail-header
  lockup + AnomalyEvidence panel + back link to /events/{eventCode}.

New components:
- AnomalyCard.razor — severity-tinted left border (signal-red on High,
  amber on Medium, neutral on Low) + SeverityBadge pill + sport icon +
  pre→post tabular-mono rate strip + relative time. Click navigates.
- SeverityBadge.razor — small pill mapping score → bucket per backend
  handoff (Low <0.45, Medium <0.60, High ≥0.60).
- AnomalyEvidence.razor — two-column pre/post panel with implied-prob
  bars + raw rates; favourite-swap callout when argmax(p_pre) ≠ argmax(p_post);
  signal-red 3px left border on the post column. Handles 2-way (no draw).

State + service split mirrors Phase 6's pattern:
- AnomalyViewModels.cs — AnomalyListItem / AnomalyDetailVm / Severity enum
  / AnomalyEvidenceSnapshot record. Severity computed in the view-model
  from Score.
- IAnomalyBrowsingService / AnomalyBrowsingService — wraps IAnomalyRepository,
  parses Anomaly.EvidenceJson into typed view-models, applies filters
  client-side. Methods: ListAsync(filter, ct), GetByIdAsync(id, ct),
  GetUnreadCountAsync(since, ct).
- AnomalyBrowsingState — Singleton holding AnomalyFilter (severity threshold,
  sport set, date range) + LastSeenUtc + cached UnreadCount. OnChange event.

Nav badge:
- NavBody.razor subscribes to AnomalyBrowsingState.OnChange, renders a
  pulsing red m-nav__badge when UnreadCount > 0. Badge resets when the
  user clicks 'Mark all read' on the feed toolbar.

Settings toggle:
- Settings.razor — added Workers:AnomalyDetectionEnabled toggle (backend
  added the flag). Localized via Settings.Worker.AnomalyDetectionEnabled.
- Marathon.UI.Services.WorkerOptions mirror — added AnomalyDetectionEnabled
  (default true).

Localization: +30 RU/EN keys following the dot-segmented convention
(Anomaly.*, Settings.Worker.AnomalyDetectionEnabled). Full key parity verified.

Tests (+31 bUnit, all passing):
- AnomalyFeedTests, AnomalyDetailTests
- AnomalyCardTests, SeverityBadgeTests, AnomalyEvidenceTests
- FakeAnomalyBrowsingService support fake registered in MarathonTestContext.

Routing: deleted the Phase 5 Pages/Anomalies.razor placeholder; new feed
page lives at Pages/Anomalies/AnomalyFeed.razor.

Build: 0 warnings, 0 errors.
Tests: Domain 109 + Application 19 + Infrastructure 80 + UI 68 = 276/276
(baseline 245, +31 new bUnit tests, no regressions).

Phase 7 status: ✅ Done (backend + frontend both complete, awaiting review).

Known deferral: AnomalyBrowsingState.LastSeenUtc is in-memory only; the
unread-count badge resets on app restart. Acceptable for now; Phase 9 may
extend ISettingsWriter or add an ILastSeenStore.

plans/initial-implementation/PLAN.md

@@ -41,7 +41,7 @@ parameter configurable.
 - [x] Phase 4: Application layer + Background workers [domain: backend] → [subplan](./phase-4-application-and-workers.md)
 - [x] Phase 5: Blazor Hybrid host + Theme + i18n [domain: frontend] → [subplan](./phase-5-host-theme-i18n.md)
 - [x] Phase 6: Event browsing UI [domain: frontend] → [subplan](./phase-6-event-browsing-ui.md)
-- [ ] Phase 7: Anomaly detection [domain: fullstack] → [subplan](./phase-7-anomaly-detection.md)
+- [x] Phase 7: Anomaly detection [domain: fullstack] → [subplan](./phase-7-anomaly-detection.md)
 - [ ] Phase 8: Results loader [domain: fullstack] → [subplan](./phase-8-results-loader.md)
 - [ ] Phase 9: Packaging + polish (final phase — full build + tests required) [domain: fullstack] → [subplan](./phase-9-packaging-polish.md)
 
@@ -69,7 +69,7 @@ parameter configurable.
 | Phase 4: Application + Workers | backend | ✅ Done | ⚠️ Pass with notes (Sonnet) | ✅ Build OK + 202/202 tests | ✅ 2acbaa5 |
 | Phase 5: Host + Theme + i18n | frontend | ✅ Done | ⚠️ Pass with notes (Sonnet, combined batch) | ✅ Build OK + 11/11 UI tests | ✅ batch (e4d8476…686550d…+) |
 | Phase 6: Event browsing UI | frontend | ✅ Done | ⚠️ Pass with notes (Sonnet) | ✅ Build OK + 228/228 tests | ✅ 553db2b |
-| Phase 7: Anomaly detection | fullstack | 🔨 Backend done | ⬜ | ✅ Build OK + 245/245 tests | ⬜ |
+| Phase 7: Anomaly detection | fullstack | ✅ Done | ⬜ | ✅ Build OK + 276/276 tests | ⬜ |
 | Phase 8: Results loader | fullstack | ⬜ Not Started | ⬜ | ⏭️ Big Bang | ⬜ |
 | Phase 9: Packaging + polish | fullstack | ⬜ Not Started | ⬜ | ⬜ | ⬜ |