Feature/lab2 - docs(lab2): git internals, signed tag, and rebase

[selysecr332]

Goal

Lab 2 submission: Git object model, reflog recovery, signed tag, rebase.

Changes

• Added submissions/lab2.md with cat-file chain, reflog recovery, tag verification, rebase logs

Testing

• git cat-file, git reflog, git tag -v, git rebase main, git push --force-with-lease

Checklist

• Title is a clear sentence (≤ 70 chars)
• Commits are signed
• submissions/labN.md updated