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

Directory.Build.props

@@ -4,8 +4,8 @@
 
     TreatWarningsAsErrors is NOT set globally because test projects carry analyzer warnings
     (e.g. xUnit1051) that would fail the build. src/ projects opt in to
-    <TreatWarningsAsErrors>true</TreatWarningsAsErrors> in their own csproj (a few still pending;
-    see #606). Once every project is clean this can be promoted back to a global default.
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors> in their own csproj — all 61 do as of #606.
+    It stays per-project rather than global only because the test projects are not yet clean.
   -->
   <PropertyGroup>
     <TargetFramework>net10.0</TargetFramework>