ci(#606): Gitea-compatible trx upload + deterministic fixes for the CI-load test flakes

- v2-ci.yml: upload-artifact@v4 -> @v3 + continue-on-error (act_runner reports as GHES and
  v4 refuses GHES, failing every run); runner-capacity diagnostic step; AKKA_TEST_TIMEFACTOR=3
  on the test step.
- Runtime/ControlPlane harnesses: akka.test.timefactor from AKKA_TEST_TIMEFACTOR
  (TestTimeFactor), single-expect-default 15s; ControlPlane gains PresenceBudget.
- Leaked spinner threads: the infinite-loop timeout tests (Calculation, Host.IntegrationTests
  RoslynVirtualTagEvaluator, 3x Core.Scripting) pinned a core for the rest of the test process
  (abandoned, never stopped). Now a bounded 5 s wall-clock spin; outer compile-inclusive bound 30 s.
- Real test races fixed: ScriptedAlarmEngine push-during-drain (Inactive is also the start
  state + persist-before-update => wait for the Cleared save); DriverReconnectE2e (both nodes
  host the driver; Created[] is last-writer-wins and ForceReconnect is a no-op while
  Connecting); ControlPlaneStarterOrder (lost-race heal waited for a 60 s refresh tick).
- Fixed sleeps -> poll-for-condition: ReconnectSupervisor LastError, Modbus deadband steps
  (wait for observed reads), Modbus dispose hygiene precondition, FOCAS probe-loop log.
- Short presence budgets -> PresenceBudget in the Runtime/ControlPlane tests seen failing on
  Gitea; Calculation Settle 10 -> 30 s. No assertion removed, nothing skipped.
- infra/README.md §10 CI; stale TreatWarningsAsErrors comment in Directory.Build.props.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs

@@ -169,8 +169,12 @@ public sealed class ModbusLifecycleHygieneTests
         var drv = new ModbusDriver(opts, "modbus-1", _ => fake);
         await drv.InitializeAsync("{}", CancellationToken.None);
 
-        // Let the probe + re-probe loops spin a few iterations.
-        await Task.Delay(200);
+        // Wait for the probe loop to issue its first send instead of sleeping a fixed 200 ms — on a
+        // loaded CI runner the loop had not run yet and the precondition below read 0 (#606). This is a
+        // presence wait (returns as soon as a send lands); the post-dispose absence window stays fixed.
+        var deadline = DateTime.UtcNow.AddSeconds(10);
+        while (Interlocked.CompareExchange(ref fake.SendCount, 0, 0) == 0 && DateTime.UtcNow < deadline)
+            await Task.Delay(10, TestContext.Current.CancellationToken);
         var sendsAtDispose = Interlocked.CompareExchange(ref fake.SendCount, 0, 0);
         sendsAtDispose.ShouldBeGreaterThan(0, "background probe loop should have issued at least one send");