feat(cms): add HomepageConfig global schema for DP-17

[jpornillos]

📝 Overview

Adds HomepageConfig global schema for Ticket #17 hero section configuration.

🚀 Type of Change

• 🐛 Bug Fix: Fixed something that was broken.
• ✨ New Feature: Added new functionality or pages.
• 🗄️ CMS / Database: Updated collections, fields, or config in Payload CMS.
• 🧹 Chore / Clean up: Text updates, typos, or code cleanup.

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🧱 CMS & Database Changes

Skip this section if no CMS or database changes were made.

• Migration Created: Ran payload migrate:create and saved the file.
• Local Verification: Verified changes in the local admin panel.

📊 Data Structure

Added heroImageDesktop, heroImageMobile, heroTitle, heroSubtitle

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🧪 Testing & Validation

• Test Case Approval: Verified that test cases were commented on the assigned GitHub issue and approved by the Project Lead before development started.
• Unit Tests: Added or updated unit test scripts covering the new logic.
• Admin Panel: Verified behavior in the CMS Admin UI.
• API Check: Tested REST/GraphQL endpoints for correct data.

📸 Visual Evidence (Mandatory)

Important

Visual proof is required to demonstrate that the approved test cases from the issue were successfully met.
Please provide screenshots, screen recordings (GIFs/Videos), or sample API outputs proving that the feature satisfies all approved test cases and do not introduce regressions.

Recording Link - Google Drive

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📋 Final Checklist

• Sync: Rebased from main and resolved conflicts.
• Pre-commit: Installed and ran pre-commit hooks successfully.
• Security: Verified no secrets or local credentials are included.
• Build: Project builds without errors.
• Visuals: Attached mandatory visual evidence proving all test cases passed.
• Migrations: Migration script included (if applicable).

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🧠 Extra Notes / Questions

Closes #17