feat: add shopify-development skill

- Add comprehensive Shopify development skill with validated GraphQL
- Fixed 4 mutations using Shopify MCP (fulfillmentCreate, appSubscription, etc.)
- Added shopify_graphql.py utilities with pagination & rate limiting
- Updated API version to 2026-01
- Added zircote/.claude as reference source

skills/shopify-development/README.md

@@ -0,0 +1,60 @@
+# Shopify Development Skill
+
+Comprehensive skill for building on Shopify platform: apps, extensions, themes, and API integrations.
+
+## Features
+
+- **App Development** - OAuth authentication, GraphQL Admin API, webhooks, billing integration
+- **UI Extensions** - Checkout, Admin, POS customizations with Polaris components
+- **Theme Development** - Liquid templating, sections, snippets
+- **Shopify Functions** - Custom discounts, payment, delivery rules
+
+## Structure
+
+```
+shopify-development/
+├── SKILL.md              # Main skill file (AI-optimized)
+├── README.md             # This file
+├── references/
+│   ├── app-development.md    # OAuth, API, webhooks, billing
+│   ├── extensions.md         # UI extensions, Functions
+│   └── themes.md             # Liquid, theme architecture
+└── scripts/
+    ├── shopify_init.py       # Interactive project scaffolding
+    ├── shopify_graphql.py    # GraphQL utilities & templates
+    └── tests/                # Unit tests
+```
+
+## Validated GraphQL
+
+All GraphQL queries and mutations in this skill have been validated against Shopify Admin API 2026-01 schema using the official Shopify MCP.
+
+## Quick Start
+
+```bash
+# Install Shopify CLI
+npm install -g @shopify/cli@latest
+
+# Create new app
+shopify app init
+
+# Start development
+shopify app dev
+```
+
+## Usage Triggers
+
+This skill activates when the user mentions:
+
+- "shopify app", "shopify extension", "shopify theme"
+- "checkout extension", "admin extension", "POS extension"
+- "liquid template", "polaris", "shopify graphql"
+- "shopify webhook", "shopify billing", "metafields"
+
+## API Version
+
+Current: **2026-01** (Quarterly releases with 12-month support)
+
+## License
+
+MIT