feat: Add interactive onboarding command (#63)

Adds a new `/core:onboard` command to provide an interactive onboarding experience for new contributors.

The command:
- Explains the repository structure and key modules.
- Lists common development commands.
- Links to good first issues.
- Includes a `--module` option for deep dives into specific modules (tenant, admin, php).
- Prompts the user about their interests to guide them to a suitable first task.

claude/code/commands/onboard.md

@@ -0,0 +1,88 @@
+---
+name: onboard
+description: Guide new contributors through the codebase
+args: [--module]
+---
+
+# Interactive Onboarding
+
+This command guides new contributors through the codebase.
+
+## Flow
+
+### 1. Check for Module-Specific Deep Dive
+
+First, check if the user provided a `--module` argument.
+
+- If `args.module` is "tenant":
+  - Display the "Tenant Module Deep Dive" section and stop.
+- If `args.module` is "admin":
+  - Display the "Admin Module Deep Dive" section and stop.
+- If `args.module` is "php":
+  - Display the "PHP Module Deep Dive" section and stop.
+- If `args.module` is not empty but unrecognized, inform the user and show available modules. Then, proceed with the general flow.
+
+### 2. General Onboarding
+
+If no module is specified, display the general onboarding information.
+
+**Welcome Message**
+"Welcome to Host UK Monorepo! 👋 Let me help you get oriented."
+
+**Repository Structure**
+"This is a federated monorepo with 18 Laravel packages. Each `core-*` directory is an independent git repo."
+
+**Key Modules**
+- `core-php`: Foundation framework
+- `core-tenant`: Multi-tenancy
+- `core-admin`: Admin panel
+
+**Development Commands**
+- Run tests: `core go test` / `core php test`
+- Format: `core go fmt` / `core php fmt`
+
+### 3. Link to First Task
+
+"Let's find a 'good first issue' for you to work on. You can find them here: https://github.com/host-uk/core-agent/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22"
+
+### 4. Ask User for Interests
+
+Finally, use the `request_user_input` tool to ask the user about their area of interest.
+
+**Prompt:**
+"Which area interests you most?
+- Backend (PHP/Laravel)
+- CLI (Go)
+- Frontend (Livewire/Alpine)
+- Full stack"
+
+---
+
+## Module Deep Dives
+
+### Tenant Module Deep Dive
+
+**Module**: `core-tenant`
+**Description**: Handles all multi-tenancy logic, including tenant identification, database connections, and domain management.
+**Key Files**:
+- `src/TenantManager.php`: Central class for tenant operations.
+- `config/tenant.php`: Configuration options.
+**Dependencies**: `core-php`
+
+### Admin Module Deep Dive
+
+**Module**: `core-admin`
+**Description**: The admin panel, built with Laravel Nova.
+**Key Files**:
+- `src/Nova/User.php`: User resource for the admin panel.
+- `routes/api.php`: API routes for admin functionality.
+**Dependencies**: `core-php`, `core-tenant`
+
+### PHP Module Deep Dive
+
+**Module**: `core-php`
+**Description**: The foundation framework, providing shared services, utilities, and base classes. This is the bedrock of all other PHP packages.
+**Key Files**:
+- `src/ServiceProvider.php`: Registers core services.
+- `src/helpers.php`: Global helper functions.
+**Dependencies**: None