Bug: Pull request not created due to existing branch reuse from previous issue automation

📝 Issue Body:

We encountered an issue during GitHub Actions run #16740435509 where the workflow attempted to create a pull request, but none was created.

Upon inspection:

A commit was successfully made (chore(dotbot): updated changes from base repo (#4)).

However, the pull request step failed silently due to:

Error: Validation Failed: ["A pull request already exists for atx/dotbot-base-changes."]

🔍 Likely Root Cause

The branch name atx/dotbot-base-changes appears to be reused across multiple issue-triggered automation runs. If an open PR already exists from this branch to dotbot-base, GitHub prevents creating another PR from the same source branch.

✅ Acceptance Criteria

[ ] Investigate if branch names are being reused across issue workflows.

[ ] If true, dynamically generate unique branch names per issue or timestamp.

[ ] Ensure PR creation step gracefully handles this and logs more clearly when skipped due to existing PR.

🧪 Suggested Fix

Append the issue number or timestamp to the branch name to ensure uniqueness:

branch_name="atx/dotbot-base-changes-${{ github.event.issue.number || github.run_id }}"

Start by locating the issue-triggered GitHub Actions workflow responsible for run #16740435509 and inspect how it sets atx/dotbot-base-changes and handles PR creation. Confirm branch names are unique per issue or run, and verify an existing-PR validation failure is logged clearly instead of failing silently.

Written by the indexing model from the issue text.