Fix/issues 582 579 581 588

[Elevate341]

What does this PR do?

This PR addresses four lifecycle and webhook issues:

• Deduplicates concurrent stopBackgroundJobs() calls and shares completion or failure.
• Defines provider conflicts: the header takes precedence, then the body, then generic.
• Includes persisted status in duplicate webhook responses without changing first-delivery responses or exposing error details.
• Exposes readonly pending and active queue counts for graceful-shutdown diagnostics.

How to test?

Run bun test to verify the full suite (504 tests). Focused lint passes for the changed TypeScript files; full bun run lint currently reports repository-wide Prettier CRLF findings.

Checklist

• My code follows the code style of this project.
• I have added tests for my changes.
• I have updated the documentation accordingly.
• I have run bun run test and bun run lint locally.

Issue Reference

Closes #582
Closes #579
Closes #581
Closes #588

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@Elevate341 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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