Add course progress contract example

[alexgduarte]

Contributes to #11

Summary

• Add a new course-progress simple contract example.
• Let the owner create course records with validated titles, descriptions, and lesson lists.
• Let learners mark lessons complete with duplicate-completion protection.
• Support learner progress reset, owner-only course archiving, ownership transfer, config updates, and paginated course-list queries.
• Include README documentation, root README navigation, schema generation, and nine focused unit tests.

Validation

• cargo fmt --manifest-path course-progress/Cargo.toml -- --check
• cargo test --manifest-path course-progress/Cargo.toml --target-dir /private/tmp/codex-course-progress-target
• git diff --check