docs: align sprint orchestration behavior with current execution flow

[numnx]

This PR brings the orchestration step documentation and UI reference pages into alignment with the existing implementation of src/domain/sprint/orchestrator/cycle-runner.ts and src/sprint/steps/protocol-step.ts.

It updates:

1. docs/sprint-loop/atomic-loop.md to show the correct execution phases and replace outdated references to mergeProtocol and actionRequiredProtocol with protocol.
2. docs-web/user/sprint-orchestration.md to sync with atomic-loop.md's cycle and state machine updates, particularly describing how a completed task fails into QA_REVIEW_FAILED correctly instead of an infinite wait.
3. docs/architecture/quality-assurance-agent.md to ensure QA_REVIEW_FAILED hold behavior aligns tightly with current code.

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PR created automatically by Jules for task 7839629614823547377 started by @numnx

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