Job Monitor: focus service boundaries and reorganize the scenario harness

[mmitche]

Parent: #17171

Tighten external contracts while preserving the pipeline-emulating harness as the final regression layer.

Scope

• Separate Azure DevOps timeline observation, durable upload ledger, and result publishing responsibilities.
• Separate Helix observation from cancellation/resubmission responsibilities.
• Avoid leaking generated service models into core reconciliation logic.
• Split the monolithic runner scenario suite by behavior area.
• Keep scripted temporal scenarios, simplify smart fakes, and add adapter-level HTTP/protocol contract tests.

Acceptance criteria

• External adapters have coherent, focused contracts.
• Core domain/planning code has no dependency on generated Helix or AzDO transport models.
• Scenario coverage remains intact and is easier to locate and extend.
• Crash/durability behavior is covered at both planner and protocol-adapter levels.