Docs - Create EasyInvoice page group with feature-specific pages

[MantisClone]

Problem

EasyInvoice is currently embedded in Use Case pages, but it should have its own dedicated documentation section with feature-specific workflow pages. Use Case pages should focus on the use case itself and link to EasyInvoice docs.

Proposed Solution

Create new "EasyInvoice" page group in docs navigation with:

• Overview (what is EasyInvoice, why use it)
• Getting Started (accessing, basic usage)
• Invoicing Workflow
• Payouts Workflow
• Subscriptions Workflow
• Dashboard & Analytics
• Forking & Customization (tutorial from Tutorial - Fork and Customize EasyInvoice #24)
• Deployment Guide (if forking)

Update Use Case pages to link to these dedicated pages instead of embedding EasyInvoice content.

Considerations

• EasyInvoice section should appear in navigation below Use Cases
• Each workflow page focuses on specific EasyInvoice features
• Use Case pages have simplified Integration Approaches tabs that link here
• Maintain separation: Use Cases = "what to do", EasyInvoice = "how to use EasyInvoice"
• Text-first approach (videos/interactive demos can be added later)

Proposed Navigation Structure

Use Cases
  - Invoicing
  - Payouts
  - etc.

EasyInvoice  <-- NEW
  - Overview
  - Getting Started
  - Invoicing Workflow
  - Payouts Workflow
  - Subscriptions Workflow
  - Dashboard & Analytics
  - Forking & Customization
  - Deployment Guide

API
  - ...