Classroom: git confusion dominates support requests

[cuihtlauac]

Parent issue: #24

Problem

Students don't know git. Merge conflicts from template updates, forgotten SSH passphrases, divergent histories — these consume instructor time. One course explicitly warns that branching is where students struggle most. Another professor had to add git config pull.rebase false to prevent confusing error messages.

Sources:

• GitHub Classroom + Codespaces lessons (merge conflicts from template updates, pull.rebase false fix)
• ECE454 Setup (branching confusion, SSH passphrase friction)
• GitHub for Courses (merge conflicts when updating assignment templates)

Proposed changes

• Add a docs/student-quickstart.md covering the minimum git commands needed for a training session (clone, add, commit, push — nothing more)
• Consider a postStartCommand or MOTD that prints a git cheat sheet on first terminal open
• Pre-configure sensible git defaults in the image (e.g., pull.rebase false, default branch name)