Add production architecture, API contract, whitepaper, and hardware roadmap docs

[ProgrammingDevelopment]

Motivation

• Provide a production-grade specification and onboarding artifacts for SigmaPrompt targeting digital twin simulation, swarm coordination, failsafe safety, and AGI-ready cognitive stacks.
• Centralize API contracts, operational NFRs, and deployment/validation guidance so engineers can implement services and integrations consistently.
• Replace an earlier long-form README section with a concise project overview that links to the new planning artifacts.

Description

• Reworked README.md into a concise project overview and added links to the new planning documents.
• Added docs/system-architecture-diagram-spec.md containing a layered C4-style diagram spec, primary dataflows, DTSL (Digital Twin Simulation Layer) components and modes, swarm coordination requirements, safety/failsafe paths, AGI cognitive stack, styling, and NFR callouts.
• Added docs/api-contract-spec.md with protocol standards, global conventions, auth, telemetry ingestion, twin simulation, swarm allocation, command/failsafe endpoints, event schemas, error envelope, and SLO targets.
• Added docs/technical-whitepaper.md as a draft technical whitepaper describing design principles, reference architecture, safety model, data governance, performance targets, and AGI-readiness; and added docs/hardware-integration-roadmap.md with phased milestones, acceptance gates, compatibility matrix, and validation tracks.

Testing

• Ran a Python link-validation check (python - <<'PY' ...) to confirm all README.md links point to existing docs/ files and the check passed successfully.

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Codex Task