docs: rename Orchestrator-Sisyphus to Atlas

[l3aro]

Summary

• Rename "Orchestrator-Sisyphus" to "Atlas" across all documentation files to prevent confusion with the Sisyphus agent

Changes

• docs/guide/overview.md: Updated 2 references ("Orchestrator-Sisyphus" → "Atlas")
• docs/guide/understanding-orchestration-system.md: Updated 6 references including Mermaid flowchart and sequence diagram labels
• docs/orchestration-guide.md: Renamed "Sisyphus (The Orchestrator)" to "Atlas (The Orchestrator)" with 6 line changes, plus minor formatting improvements

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Summary by cubic

Renamed the orchestrator from “Orchestrator-Sisyphus” to “Atlas” across documentation to reduce confusion with the Sisyphus-Junior agent. Updates include text, tables, and Mermaid/sequence diagram labels; no code or config changes.

^{Written for commit 3268782. Summary will update on new commits.}

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[l3aro]

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[cubic-dev-ai]

No issues found across 3 files