Fix deterministic CI failures across active pull requests

[Aaronontheweb]

Summary

This PR fixes deterministic and race-prone failures found across #1988, #1987, and #1981.

• The PID watchdog now uses TimeProvider and a completion signal.
• The SignalR client tests now use TestServer without loopback ports.
• The MCP stdio tests now use the repository smoke server without npm.
• The PowerShell retry tests now wait for virtual timer creation.
• The PowerShell elapsed result now uses the injected clock.
• The skill order test no longer asserts an unrelated skill version.
• Dependabot now ignores the incompatible Roslyn 5.9.0 update.

PR #1989 now owns its seed-batch fix. This PR does not duplicate that change.

The Roslyn 5.9.0 package requires an unavailable analyzer build. Its generator also conflicts with the current SDK compiler.

Validation

• dotnet restore Netclaw.slnx
• dotnet build Netclaw.slnx -c Release --no-restore
• Full suite: 7,550 passed, 15 skipped, and 0 failed.
• SignalR group: five repeated passes.
• PID watchdog group: ten repeated passes.
• PowerShell probe group: ten repeated passes.
• MCP stdio group: two repeated passes.
• dotnet slopwatch analyze
• pwsh ./scripts/Add-FileHeaders.ps1 -Verify
• Changed C# files passed the focused whitespace check.