docs: add project documentation, memory, and setup guides

MEMORY.md

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+# Project Memory
+
+## Project Context
+This project (`product_inventory`) integrates Google Sheets with Shopify. It serves as a master inventory management tool where users edit product data in a Google Sheet, and scripts automatically sync those changes to Shopify.
+
+**Critical Components:**
+- **Google Apps Script**: Runs the logic.
+- **"vars" Sheet**: Holds all configuration and API keys. NEVER hardcode credentials.
+- **Shopify Admin API**: Used for syncing. REST for Orders, GraphQL for Products.
+
+## Work Patterns & Agreements
+1.  **Documentation First**: Before implementing complex features, we update the plan and often the documentation (README/ARCHITECTURE).
+2.  **Safety First**: We use `SafeToAutoRun: false` for commands that deploy or modify external state until verified.
+3.  **Strict Typing**: We use TypeScript. No `any` unless absolutely necessary (and even then, we try to avoid it).
+4.  **Artifact Usage**: We use `task.md`, `implementation_plan.md`, and `walkthrough.md` to track state.
+
+## Key Technical Decisions
+- **Queue System**: We implemented `onEditQueue.ts` to batch edits. This prevents hitting Shopify API rate limits and Google Apps Script execution limits during rapid manual edits.
+- **Hybrid API**: We use REST for retrieving Orders (legacy/easier for flat data) and GraphQL for Products (more efficient/flexible).
+- **Global Exports**: Functions in `src/global.ts` are explicitly exposed to be callable by Apps Script triggers.
+
+## User Preferences
+- **OS**: Windows.
+- **Shell**: PowerShell.
+- **Node Manager**: `fnm`.