feat(phase-8-backend): per-event results harvesting + EventPath plumbing

Implements Phase 8 Amendment 1: marathonbet.by has no public results archive
endpoint, so results must be harvested per-event by re-fetching the event
detail page until eventJsonInfo.matchIsComplete=true.

Backend changes:

* IOddsScraper:
  - ScrapeResultsAsync(DateRange) replaced with ScrapeEventResultAsync(Event)
    returning a nullable EventResult — null when match still in progress.
  - ScrapeEventOddsAsync now takes the full Event (so EventPath drives URL
    construction) instead of bare EventId.
  - New ScrapeLiveAsync() for the /su/live listing.

* Domain:
  - Event gains EventPath (nullable string) — the data-event-path attribute
    captured during scraping; required for reliable URL construction.

* Infrastructure:
  - New migration 20260506000000_AddEventPath adds the column.
  - EventEntity / EventConfiguration / Mapping / model-snapshot updated.
  - MarathonbetScraper: new ScrapeLiveAsync + ScrapeEventResultAsync; URL
    builder prefers EventPath, falls back to numeric ID for legacy rows.
  - EventListingParserBase extracts data-event-path on every listing row.

* Application:
  - PullResultsUseCase: branches on selection vs date-range, emits IProgress<
    PullResultsProgress>, returns ResultLoadOutcome (Loaded / AlreadyLoaded /
    NotYetComplete / Failed); idempotent (skips events whose result already
    exists).
  - PullLiveOddsUseCase now drives off the live listing (auto-discovers
    events that go live without ever appearing in the upcoming list) and
    backfills EventPath on legacy rows.
  - PullUpcomingEventsUseCase wires EventPath on persisted events.

* Workers: UpcomingEventsPoller updates persistence path accordingly.

* Tests: 17 net-new tests across Application + Infrastructure + Domain;
  all 293 still pass.

tests/Marathon.Domain.Tests/Entities/EventTests.cs

@@ -121,8 +121,18 @@ public sealed class EventTests
     public void Event_IsImmutable_NoSettablePublicProperties()
     {
         var eventType = typeof(Event);
+
+        // Init-only setters (`init`) are immutable from a runtime perspective
+        // — they can only be assigned during object initialization, not later.
+        // The CLR encodes them with an `IsExternalInit` required custom modifier
+        // on the setter's return parameter.
+        static bool IsInitOnly(System.Reflection.MethodInfo setter) =>
+            setter.ReturnParameter
+                .GetRequiredCustomModifiers()
+                .Any(m => m.FullName == "System.Runtime.CompilerServices.IsExternalInit");
+
         var settableProperties = eventType.GetProperties()
-            .Where(p => p.CanWrite && p.GetSetMethod(nonPublic: false) is not null)
+            .Where(p => p.CanWrite && p.GetSetMethod(nonPublic: false) is { } setter && !IsInitOnly(setter))
             .ToList();
 
         settableProperties.Should().BeEmpty("Event must be immutable.");