Restructure documentation for DRY principle

Split documentation into three files to eliminate duplication:
- ARCHITECTURE.md: Shared technical documentation (domain models,
  services, database schema, workflows, patterns)
- CLAUDE.md: Claude Code-specific context referencing ARCHITECTURE.md
- AGENTS.md: Codex agent context referencing ARCHITECTURE.md

This allows both Claude Code and Codex CLI to share the same source
of truth for architecture details while maintaining tool-specific
configuration in separate files.

Benefits:
- Single source of truth for technical details
- Easier maintenance (update once, not twice)
- Consistent documentation across tools
- Clear separation of concerns

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,121 @@
+# MoneyMap - Claude Code Context
+
+## Quick Overview
+
+MoneyMap is an ASP.NET Core 8.0 Razor Pages application for personal finance tracking. Users can import bank transaction CSVs, categorize expenses, attach receipt images/PDFs, and parse receipts using OpenAI's Vision API.
+
+## Architecture Documentation
+
+**For detailed technical documentation, see [ARCHITECTURE.md](./ARCHITECTURE.md)**
+
+The architecture document contains:
+- Complete technology stack
+- Core domain models (Transaction, Receipt, Card, Account, Merchant, etc.)
+- Service layer details (TransactionImporter, CardResolver, TransactionCategorizer, etc.)
+- Database schema and relationships
+- Key workflows and design patterns
+- Security and performance considerations
+
+## Project Structure
+
+```
+MoneyMap/
+├── Data/
+│   └── MoneyMapContext.cs          # EF Core DbContext
+├── Models/
+│   ├── Account.cs                  # Bank accounts
+│   ├── Card.cs                     # Payment cards
+│   ├── Merchant.cs                 # Merchants/vendors
+│   ├── Transaction.cs              # Core transaction entity
+│   ├── Receipt.cs                  # Receipt files
+│   ├── ReceiptLineItem.cs          # Parsed line items
+│   └── ReceiptParseLog.cs          # Parse attempt logs
+├── Services/
+│   ├── TransactionCategorizer.cs   # Auto-categorization logic
+│   ├── ReceiptManager.cs           # Receipt upload/storage
+│   └── OpenAIReceiptParser.cs      # AI-powered receipt parsing
+├── Pages/
+│   ├── Index.cshtml[.cs]           # Dashboard
+│   ├── Upload.cshtml[.cs]          # CSV import
+│   ├── Transactions.cshtml[.cs]    # Transaction list
+│   ├── EditTransaction.cshtml[.cs] # Edit transaction
+│   ├── ViewReceipt.cshtml[.cs]     # Receipt details
+│   ├── CategoryMappings.cshtml[.cs]# Category rules
+│   ├── Merchants.cshtml[.cs]       # Merchant management
+│   └── Recategorize.cshtml[.cs]    # Bulk recategorization
+└── Program.cs                      # DI configuration
+```
+
+## Common Development Tasks
+
+### Adding a New Page
+1. Create `.cshtml` and `.cshtml.cs` files in `Pages/`
+2. Inherit from `PageModel`
+3. Add route via `@page` directive
+4. Register dependencies in constructor via DI
+
+### Adding a New Service
+1. Create interface in appropriate namespace
+2. Create implementation class
+3. Register in `Program.cs`:
+   ```csharp
+   builder.Services.AddScoped<IMyService, MyService>();
+   ```
+
+### Adding a Database Migration
+```bash
+dotnet ef migrations add MigrationName
+dotnet ef database update
+```
+
+### Modifying Domain Models
+1. Update model class in `Models/`
+2. Update `MoneyMapContext.OnModelCreating()` if needed (relationships, indexes)
+3. Create and apply migration
+
+## Key Design Principles
+
+1. **Service Layer Pattern**: Business logic lives in services, not pages
+2. **Result Pattern**: Services return result objects (not exceptions)
+3. **Dependency Injection**: All services injected via interfaces
+4. **Single Responsibility**: Each service has one clear purpose
+5. **Clean Architecture**: UI → Services → Data Access
+
+## Important Notes
+
+- **Duplicate Prevention**: Transactions have a unique constraint on (Date, Amount, Name, Memo, AccountId, CardId)
+- **Cascade Deletes**: Deleting a transaction cascades to receipts, parse logs, and line items
+- **Merchant Assignment**: Category mappings can auto-assign merchants to transactions
+- **Transfer Detection**: Transactions with `TransferToAccountId` are identified as transfers
+- **Receipt Parsing**: OpenAI API key required for receipt parsing (env var `OPENAI_API_KEY`)
+
+## Development Workflow
+
+1. Read [ARCHITECTURE.md](./ARCHITECTURE.md) for technical details
+2. Make changes to models, services, or pages
+3. Test locally
+4. Create database migration if schema changed
+5. Commit with descriptive message
+
+## Configuration
+
+See `appsettings.json`:
+- `ConnectionStrings:MoneyMapDb` - SQL Server connection
+- `OpenAI:ApiKey` - OpenAI API key (optional, use env var instead)
+- `Receipts:StoragePath` - Receipt storage location (relative to wwwroot)
+
+## Testing
+
+- All services use interfaces for mockability
+- Use in-memory database for integration tests
+- Mock `IReceiptParser` to avoid OpenAI API calls in tests
+
+## Questions?
+
+Refer to [ARCHITECTURE.md](./ARCHITECTURE.md) for comprehensive technical documentation including:
+- Detailed service descriptions
+- Database schema
+- Key workflows
+- Security considerations
+- Performance optimizations
+- Troubleshooting guide