full-day workshop: Add the missing commit step before creating the feature pull request

Problem

In content/full-day/7-github-flow.md, learners create add-filter, run git add ., select Generate Commit Message, press Enter, and then run git push -u origin add-filter. No git commit command or Source Control commit action is provided.

Generating a commit message does not itself create a commit. The branch therefore has no commits ahead of main, and gh pr create can fail because there are no commits between the branches. This blocks the pull-request portion of the workshop.

Suggested change

Add an explicit commit action after generating the message, and verify the branch is ahead of main before pushing and opening the PR.

Acceptance criteria

• Learners are told exactly where the generated message appears.
• An explicit CLI or Source Control commit step is included.
• The instructions verify the feature commit exists on add-filter.
• git push publishes the feature commit.
• gh pr create succeeds from a fresh workshop run.

Open content/full-day/7-github-flow.md and follow the workshop sequence around add-filter, Generate Commit Message, git push, and gh pr create. Add the missing commit and verification instructions so a fresh run confirms the feature commit is ahead of main, pushes it, and successfully creates the pull request.