fix project documentation + one bit of domain->context transition

[fabnemEPFL]

This pull request updates the course documentation and site generation to improve clarity, update terminology, and add a new project brief. The most significant changes include the addition of a new dengue early-warning project, a redesign of how project briefs are displayed, consistent terminology updates from "domain" to "context," and improvements to assessment and submission instructions.

Project documentation and site structure improvements:

• Added a new project brief: Project 6: AI-Powered Dengue Early-Warning Platform with detailed requirements and proof-of-concept expectations (content/project-documentation/projects/project-6-dengue-early-warning.md).
• Refactored the project briefs overview: all project briefs are now displayed on a single tabbed overview page instead of separate pages, with updated navigation and summary table generation in build_site.py and documentation (content/project-documentation/README.md, build_site.py). [1] [2] [3] [4]

Terminology and content consistency:

• Updated terminology throughout the course overview and schedule from "domain lecture" and "domain themes" to "context lecture" and "context themes" for improved clarity (content/pages/home.md). [1] [2] [3] [4] [5] [6] [7]

Assessment and submission clarity:

• Clarified the weight of milestones and final submission as both a percentage of the course grade and of the project grade (content/project-documentation/student/milestone-1-technical-design-and-repository.md, content/project-documentation/student/final-submission.md). [1] [2]
• Replaced individual contribution reports with a single, team-signed contribution statement for the final submission, updating instructions and recommended file location (content/project-documentation/student/final-submission.md). [1] [2] [3]

Other updates:

• Updated the weekly checkpoint reference from week 10 to week 11 in documentation and site build order (build_site.py, content/project-documentation/README.md). [1] [2]
• Minor UI improvement: added scroll-margin-top to .section in assets/site.css for better anchor navigation.