fix(tests): prevent ChatViewModel cancellation from aborting test host

[YoungSx]

Summary

Fixes #139.

• Treats store-projection cancellation caused by ChatViewModel.Dispose() as a normal terminal condition, while preserving caller-owned cancellation and real faults.
• Adds a deterministic regression that previously reproduced the AsyncRelayCommand thread-pool rethrow / exit 134 test-host crash.
• Replaces the two VoiceInput test doubles that raced the background signal poller with an AsyncLocal dispatcher scope and explicit authorization-help synchronization.

Verification

• dotnet build tests/SalmonEgg.Presentation.Core.Tests/SalmonEgg.Presentation.Core.Tests.csproj -c Debug
• VoiceInputDiagnosticsProbeViewModelTests: 10 consecutive runs, each 13/13 passed.
• New Chat cancellation regression: passed.
• Full SalmonEgg.Presentation.Core.Tests:
  • before rebase: 2 runs, each 3278/3278 passed
  • after rebasing onto current develop: 3286/3286 passed
• Reverse verification: disabling the lifecycle-cancellation guard restored the original TaskCanceledException, exit 134, and failed: 0 / total: 0 host-abort signature.

The branch was rebased directly onto the latest origin/develop before the final full-suite run, so it is currently fast-forward mergeable unless develop advances again.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
salmonegg	Ready	Preview	Sep 1, 2026 7:04pm UTC

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