fix(firewall): use Core.Now on the game thread; seed the test clock

Firewall.LoadFrom and ToSettings run on the game loop (Configure sweep, the
maintenance timer, Save on shutdown) but read DateTime.UtcNow. ToSettings was
the one that mattered: it derives each persisted expiry as
now + (expiresAtTick - nowTicks) while nowTicks came from Core.TickCount, so
pairing a fresh wall clock with the loop's tick baked the loop's lag into every
saved TTL. Core.Now and Core.TickCount are refreshed together at the top of each
iteration, so taking both keeps the operands on one instant.

Left DateTime.UtcNow in CrowdSecAlertClient and the reporter's flush/drain
paths, which run on the pool and have no loop clock to read.

Neither test fixture seeded Core._now, so Core.Now was DateTime.MinValue for the
whole test host -- MinValue.AddHours(-1) throws, and any code correctly reading
the game-thread clock computed nonsense. Seed it as Main.cs does.

Also fixes a dangling collection reference: the firewall tests moved into
UOContent.Tests still declared [Collection("Sequential Server Tests")], which is
only defined in Server.Tests. xUnit matched no fixture and silently skipped the
bootstrap for those tests.

Comment pass over the branch: drop development narration and tighten what stays.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Projects/Server.Tests/Fixtures/TestServerInitializer.cs

@@ -1,3 +1,4 @@
+using System;
 using System.IO;
 using System.Reflection;
 using System.Threading;
@@ -78,6 +79,10 @@ internal static class TestServerInitializer
             Core.LoopContext = new EventLoopContext();
             Core.Expansion = Expansion.EJ;
 
+            // Seed the loop clock as Main.cs does before the Configure sweep; otherwise Core.Now is
+            // DateTime.MinValue for the whole test host.
+            Core._now = DateTime.UtcNow;
+
             // Timer wheel must exist before NetState.Configure(), which schedules a recurring
             // sweep via Timer.DelayCall (matches production ordering in Main.cs: Timer.Init runs
             // before AssemblyHandler.Invoke("Configure")).