Isolate manual webhook resilience claims from hosted workers

[Chris0Jeky]

The webhook resilience tests manually claim and transition real SQLite delivery rows, but their base fixture also started the webhook worker. A worker could claim an immediately due row before the test, producing the observed attempt-1 claim failure in #2851.

Use the existing HostedWorkerDisabledTestWebApplicationFactory for this class. All four tests retain their repository assertions; production workers and worker-dependent test classes are unchanged.

Refs #2853. One file, five additions and three deletions.

Validation:

• All four WebhookDeliveryResilienceTests plus the existing live-service fixture isolation contract: 5 passed, no skips.
• Independent Terra review: SHIP; all four cases manually drive repository state, no worker dispatch scenario is removed. Reviewer ran no tests.
• Full backend: dotnet test backend/Taskdeck.sln -c Release -m:1 passed 9141 tests with 5 declared skips, exit 0, at 5d7e3ad.

No controlled runtime replay of the original scheduling race is claimed. The passing isolation contract verifies worker removal while retaining the web host. OUTSTANDING_TASKS.md is unchanged.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-09T22:17:01.837460Z	5d7e3ad	PR opened

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[Chris0Jeky]

Terra independent review: SHIP, all four tests manually drive real repository/EF state and none requires hosted dispatch; assertions unchanged. Full backend passed9141/5 skipped, focused webhook plus live fixture-isolation contract5/5. Two logs hash-preserved under .claude/local/milestone-20260909/preserved-2853-webhook/.tmp/issue-2853/; plain worktree removal succeeded after ignored inventory. Included in #2851 for qualification and delivery; no independent merge requested.