fix(server): expose stopped task results

[yltx]

Summary

• expose retained round results when a task finishes as stopped
• return the same stopped-task summary through status polling and WebSocket completion
• preserve cancellation semantics: WebSocket success stays false and cooperative stops keep error null
• expose an explicit empty summary when cancellation happens before the first completed round

Contract

Stopped tasks now expose total_runs, success_runs, and full details instead of hiding retained results behind a null result.

TDD

The first cancellation regression failed on origin/main because TaskManager.get_status() returned a null result. The production change only extends the existing terminal-result projection to TaskStatus.STOPPED.

Verification

• focused task tests: 20 passed
• complete suite with coverage: 586 passed
• Ruff check: passed
• Ruff format: passed
• codespell: passed
• diff-cover against origin/main: 100% patch coverage

Scope

Only autowsgr/server/task_manager.py and its focused tests are changed. This PR does not alter scheduler behavior, decisive error mapping, response schemas, native types, or device leasing.

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[yltx]

Coverage verification:

• GitHub Pytest run completed successfully with 586 passed.
• The CI Codecov uploader found coverage.xml and queued SHA 24625d9 successfully: https://app.codecov.io/github/openwsgr/autowsgr/commit/24625d9eceef107bfe6d579966d643a936d45240
• Codecov test-results upload also queued successfully.
• GitHub currently has no Codecov check/status for this SHA; this is absence of an external result, not a reported Codecov success or failure.
• Equivalent local patch gate against origin/main: uvx diff-cover coverage.xml --compare-branch origin/main --fail-under=53.17
• Result: 1 changed executable line, 0 missing, 100% patch coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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