fix(agent): Add section on workspace structure

The agent used to trip itself up when looking for code. With this
section, that doesn't happen any more.

AGENTS.md

@@ -176,6 +176,21 @@ After making ANY code change, you MUST run these commands and fix any issues:
 
 ## Project Structure Guidelines
 
+### Workspace Structure
+
+This project is a Cargo workspace containing three crates:
+
+- **banks2ff/**: Main CLI application (source in `banks2ff/src/`)
+- **firefly-client/**: Standalone Firefly III API client library (source in `firefly-client/src/`)  
+- **gocardless-client/**: Standalone GoCardless API client library (source in `gocardless-client/src/`)
+
+**Navigation Guidelines:**
+- Always identify which crate contains the relevant code before searching or editing
+- Use the root `Cargo.toml` workspace members to confirm crate boundaries
+- For main application logic: look in `banks2ff/src/`
+- For API client implementations: check `firefly-client/src/` or `gocardless-client/src/` as appropriate
+- When uncertain, search across the entire workspace using tools like `grep` with appropriate paths
+
 ### Core Module (`banks2ff/src/core/`)
 - **models.rs**: Domain entities (BankTransaction, Account)
 - **ports.rs**: Trait definitions (TransactionSource, TransactionDestination)