docs: expand troubleshooting section with additional edge cases

[q-soriarty]

Problem

The Troubleshooting section currently covers 5 scenarios:

1. Accidental direct commit to protected branch
2. Forgot to pull before branching
3. Squash-merged instead of merge-committing
4. Force-pushed to a shared branch
5. Cherry-pick to another branch

Additional real-world scenarios are missing:

• "I merged the wrong branch into develop/main"
• "I need to undo a merge that was already pushed"
• "I created a branch from main instead of develop"
• "My PR has merge conflicts — how do I resolve them in Gitflow?"
• "I accidentally deleted a branch before it was merged"
• "I committed secrets/credentials — how do I clean up?"

Expected behavior

Add recovery steps for the most common additional scenarios. Prioritize by likelihood and severity.

[github-actions]

Closed by #85 (merged into develop).