docs: add CLAUDE.md for project guidance and setup instructions

Author: mattobee

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a Sanity Studio instance for Eventua11y, managing content for the eventua11y.com website. It's a headless CMS built with Sanity v3 that handles accessibility-focused event data.
+
+## Common Commands
+
+### Development
+- `npm run dev` - Start development server
+- `npm run start` - Start production server  
+- `npm run build` - Build the studio
+- `npm run deploy` - Deploy to Sanity hosting
+- `npm run deploy-graphql` - Deploy GraphQL schema
+
+### Code Quality
+- Prettier is configured with: semi: false, printWidth: 100, bracketSpacing: false, singleQuote: true
+- ESLint uses @sanity/eslint-config-studio v5.0.2
+
+## Architecture
+
+### Multi-Environment Setup
+The studio is configured for two environments in `sanity.config.js`:
+- **Production** (`/production`): dataset 'production', project ID '2g5zqxo3'
+- **Development** (`/test`): dataset 'test', project ID '2g5zqxo3'
+
+### Schema Structure
+Content types are defined in `/schemas/` and exported via `/schemas/index.js`:
+- `event` - Core event schema with complex conditional fields
+- `course` - Course/training content
+- `provider` - Event providers/organizers
+- `person` - Speaker profiles
+- `collection` - Event collections
+- `book` - Resource books
+
+### Key Plugins
+- `@sanity/cross-dataset-duplicator` - Event duplication between environments
+- `sanity-plugin-country-state-select` - Location selection
+- `sanity-plugin-recurring-dates` - Recurring event dates
+- `@sanity/vision` - GROQ query testing
+- `@sanity/google-maps-input` - Geographic data entry
+
+### Event Schema Complexity
+The event schema (`/schemas/event.js`) has sophisticated conditional logic:
+- Parent/child event relationships
+- Conditional field visibility based on event type
+- Theme vs normal event types
+- Attendance mode affects location field visibility
+- Call for speakers with closing dates
+- Scheduled vs unscheduled events
+
+### Content Relationships
+- Events can reference speakers (person type)
+- Events can have parent-child relationships
+- Cross-dataset duplication for events between environments