Add a "Complete Lesson" button at the end of every lesson

Problem

Learners need a clear and consistent way to mark a lesson as completed after finishing its content.

Currently, progress tracking is visible on the website, but completing a lesson should be an explicit action available at the end of each lesson.

Proposed solution

Add a "Complete Lesson" button at the bottom of every lesson page.

When the learner clicks the button:

• Mark the current lesson as completed.
• Persist the completion state locally.
• Update the completed-lessons counter and progress bar.
• Change the button state to something like "Completed ✓".
• Prevent duplicate completion actions if the lesson is already marked as completed.

Suggested UX

• Place the button after the final lesson section, quiz, exercise, or artifact.
• Use a visually clear primary button style.
• Show a short confirmation message after completion.
• Allow learners to unmark a lesson later if needed.

Acceptance criteria

• Every lesson has a completion button at its end.
• Clicking the button updates the lesson completion state.
• Progress counters update immediately without requiring a page refresh.
• Completion state remains available after reloading the website.
• Completed lessons have a clear visual state.
• The feature works on both desktop and mobile layouts.

Why this matters

A visible completion action gives learners a stronger sense of progress and makes it easier to follow the curriculum in sequence.