Add API contract guide, split spec template, finalize grading system - New API-Contract-Guide.md: explains HTTP/API basics from scratch, why backend and frontend need a contract, what backend must document and when, what frontend needs and when, a worked endpoint example from docs/examples/example_module, and a reconciliation checklist. - Getting-Started.md: specification.md replaced with separate specification-backend.md / specification-frontend.md per module (chosen so contract mismatches are a real, checkable thing), links to the new guide. - Home.md: add API contract guide to the navigation list. - Grading-System.md: fill in the full 100-point breakdown (15+10+20+10+35+10), with defense in Module 3 serving as the exam, backend/frontend graded separately except for the joint integration score.