Add initial plugin implementation and development setup

CLAUDE.md

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+# @xtr-dev/payload-notifications Development Guide
+
+## Project Overview
+
+This is a PayloadCMS plugin that adds a configurable notifications collection. The plugin allows developers to:
+- Create notifications with titles and rich text messages
+- Configure relationship attachments to any collection
+- Track read/unread status
+- Target specific recipients
+
+## Architecture
+
+### Plugin Structure
+```
+src/
+├── index.ts              # Main plugin export
+├── types.ts              # TypeScript interfaces
+├── collections/
+│   └── notifications.ts  # Notifications collection schema
+└── utils/
+    └── buildFields.ts    # Dynamic field builder for relationships
+```
+
+## Development Guidelines
+
+### Code Style
+- Use TypeScript for all files
+- Follow PayloadCMS plugin conventions
+- Use descriptive variable and function names
+- Add JSDoc comments for public APIs
+
+### Plugin Configuration
+The plugin accepts a configuration object with:
+- `collections`: Collection settings (slug, labels)
+- `relationships`: Array of relationship configurations
+- `access`: Custom access control functions
+- `fields`: Additional custom fields
+
+### Relationship System
+- Relationships are stored in an `attachments` group field
+- Each relationship is dynamically generated based on config
+- Supports single and multiple selections (`hasMany`)
+
+### Collection Schema
+The notifications collection includes:
+- Required fields: title, message, recipient
+- Optional fields: isRead, readAt, attachments
+- Automatic timestamps: createdAt, updatedAt
+
+## Testing Strategy
+- Test with different PayloadCMS versions
+- Verify relationship configurations work correctly
+- Test access control functionality
+- Ensure TypeScript types are accurate
+
+## Build Process
+- Use TypeScript compiler for builds
+- Generate declaration files (.d.ts)
+- Bundle for both CommonJS and ES modules
+- Include source maps for debugging
+
+## Plugin Registration
+The plugin should be registered in PayloadCMS using the standard plugin pattern:
+```typescript
+export const notificationsPlugin = (options: NotificationsPluginOptions = {}) => {
+  return (config: Config): Config => {
+    // Plugin implementation
+  }
+}
+```
+
+## Key Implementation Notes
+1. Use PayloadCMS field types and validation
+2. Leverage PayloadCMS access control patterns
+3. Generate relationship fields dynamically based on config
+4. Provide sensible defaults for all configuration options
+5. Ensure plugin doesn't conflict with existing collections