Add Process tab context menu actions

[PrimeBuild-pc]

Summary

Adds a lightweight right-click context menu to the Process tab process list. The menu reuses existing safe ViewModel and service paths for affinity, CPU Sets clearing, CPU priority, memory priority, process info refresh, opening executable location, and copying process details.

Changes

• Adds a DataGrid row context menu for Process tab process rows.
• Wires Apply Affinity through a row-specific ApplyContextAffinityCommand that selects the row process and delegates to IProcessAffinityApplyCoordinator.ApplyCoreSelectionAsync.
• Wires CPU priority actions to IProcessService.SetProcessPriority guardrails, with Realtime shown disabled and High retaining the existing warning behavior.
• Wires memory priority actions to IProcessMemoryPriorityService.SetMemoryPriorityAsync with safe user-message failures.
• Adds safe selected-process summary refresh after context actions.
• Adds open executable location validation and copy-process-info clipboard support.
• Adds ViewModel tests for the menu-backed commands and confirms context actions do not create persistent rules.

Validation

• dotnet test "ThreadPilot_1.sln" --configuration Release --no-restore
• Result: Passed, 328 passed, 0 failed, 0 skipped.

Notes

No version bump, tag, release notes, persistent rule creation, rules editing UI, save-as-rule flow, affinity core logic, memory-priority backend logic, diagnostics changes, or Process tab redesign are included.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 46.99454% with 97 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
ViewModels/ProcessViewModel.Behaviors.partial.cs	47.50%	70 Missing and 14 partials ⚠️
ViewModels/ProcessViewModel.cs	55.55%	8 Missing ⚠️
Views/ProcessView.xaml.cs	0.00%	5 Missing ⚠️

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