Add end-to-end architecture blueprint for Shopify ↔ GHL SaaS integration

[LiveAI-CEO]

Motivation

• Provide a single, locked architecture spec before implementation for a two-app SaaS integration (Shopify public app + GoHighLevel public app) to avoid rework.
• Capture the full Supabase data model, OAuth/token lifecycle, PII sync edge cases, webhook/idempotency strategy, asset deployment model, and marketplace compliance requirements.
• Make design decisions explicit so engineers can implement migrations, auth, and sync code against a stable blueprint.

Description

• Added SAAS_INTEGRATION_ARCHITECTURE.md, a comprehensive architecture blueprint that defines the complete Supabase schema (tables, columns, relationships, indexes, RLS recommendations, and partitioning guidance).
• Documented end-to-end OAuth flows for Shopify and GHL including state/PKCE handling, token persistence and rotation (oauth_connections / oauth_tokens), refresh logic, and disconnect/reauth handling.
• Added sync pipeline constructs including mapping/matcher tables (field_mappings, identity_links), reliable ingestion (webhook_receipts, sync_events, sync_actions, dead_letter_queue), asset deployment tables, and operational controls for rate-limiting and PII safety.
• Included marketplace compliance and approval risk checklist for Shopify and GHL plus a recommended implementation order to minimize rework.

Testing

• Created and inspected the file SAAS_INTEGRATION_ARCHITECTURE.md and validated its contents with nl -ba SAAS_INTEGRATION_ARCHITECTURE.md | sed -n checks which succeeded.
• Performed repository operations git add and git commit which succeeded and recorded the new file.
• Ran lightweight repository checks (rg --files, find, git status --short) used to validate workspace context which all returned successfully.
• This is a documentation-only change so no unit/integration tests were required or executed against runtime code.

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Codex Task