Fullscreen button

[RrOoSsSsOo]

🚀 Pull Request

📝 Description

Add a fullscreen button to have, in browser tab or in PWA mode, the fullscreen.

🛠️ Changes Implemented

• Add the fullscreen button and his code.

🧪 Testing Strategy

• Run ./gradlew test
• Create a custom Docker Image that I run in selfhosted

📸 Visual Changes (if applicable)

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⚠️ Required Pre-Submission Checklist

• Code adheres to project style guidelines and conventions
• Branch synchronized with latest develop branch (please resolve any merge conflicts)
• 🚨 CRITICAL: Automated unit tests added/updated to cover changes (MANDATORY for ALL Spring Boot backend and Angular frontend changes - this is non-negotiable)
• 🚨 CRITICAL: All tests pass locally (run ./gradlew test for Spring Boot backend, and ng test for Angular frontend - NO EXCEPTIONS)
• 🚨 CRITICAL: Manual testing completed in local development environment (verify your changes work AND no existing functionality is broken - test related features thoroughly)
• Flyway migration versioning follows correct sequence (if database schema was modified)
• Documentation PR submitted to booklore-docs (required for features or enhancements that introduce user-facing or visual changes)

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💬 Additional Context (optional)