feat: add pdf learning workspace

[Santirv17]

In order to make pdf teaching and learning more interactive and engaging, this PR adds a learning workspace next to PDFs in player mode.

• Includes teacher-authored instructions, private notes, and learning goals with self-reported progress.

• Add PDF settings in Builder for instructions and goal management.

• Allow teachers to add, edit, delete, and drag goals to reorder them.

• Add a collapsible and resizable desktop panel and a temporary drawer on smaller screens.

• Coordinate the workspace with chat and pinned content.
• Keep the existing PDF viewer and PDF description behavior.

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.2% Duplication on New Code

See analysis details on SonarQube Cloud