Fix output capture races and bound stalled CI tests

[Sev7eNup]

What and why

CI exposed both timing-dependent tests and actual output loss: startProgram stopped reading five seconds after the child exited even while it was still collecting buffered stderr. A delayed reader could therefore return a successful result with missing lines. A stalled backend run also kept Actions occupied for more than 23 minutes without identifying the stuck test.

Changes

• Renew the post-exit drain grace when bytes are captured. Discarded output beyond the cap does not renew it, and process timeout plus grace remains a hard total bound. Keep the incomplete-capture warning and document the behavior in German and English.
• Add delayed-reader regression cases for complete capture and the hard total bound. The capture case failed before the fix.
• Render each website variant in a shared fixture with a 30-second build limit, then check publication and route isolation under the normal test limit.
• Use a start signal and a test-controlled gate for PowerShell cancellation, with asynchronous cancellation and bounded waits. Verify a background process is still alive instead of measuring startup speed. Compare cron forecasts with request time.
• Stop hung test hosts after two minutes without test progress and retain their sequence and diagnostic minidump. Limit the backend test step to 10 minutes and its job to 15 minutes.
• Cap MSBuild test projects at two concurrent runs. The VSTest container limit alone did not enforce this: the failed runner started four projects together. Extend the configuration guard to cover this separate limit.

No retries or skipped checks are added.

Validation

• All 220 website tests and strict ESLint pass.
• All 10 OperationalKnowledgeReader tests pass.
• All 34 affected startProgram and runspace tests pass with coverage and the hang-detection options, including Windows PowerShell 5.1 capture and cleanup tests.
• Both test-run configuration guards pass through the solution-level command with the MSBuild concurrency cap.
• The complete local Engine suite passed before the additional drain fix (2,620 passed, 10 provider tests skipped); CI validates the final combined change.

Unrelated Dependabot Quartz API incompatibilities are outside this change.