TODO: Handle Error for Existing Branch on Word Submission

When a user submits a new word or edits an existing word in the dictionary, the system should check if the branch already exists before attempting to create a new branch. Currently, if a branch with the same name already exists, the submission process fails without providing a clear error message to the user.

https://github.com/babblebey/jargons.dev/blob/0eeb366b4346c28a400586082fadb331c0ee342f/src/lib/branch.js#L10

**Proposed Solution:**
1. Add a check in the submission process to verify if the branch already exists. (but this will assume that a fork has already been created before-hand)
2. If the branch exists, display a user-friendly error message indicating that the word already exists in the dictionary.
3. Provide guidance on how to proceed, such as editing the existing word instead of creating a new one.

**Additional Notes:**
- Important to state that the proposed solution is pretty much me thinking out loud, I have some thought which really looks like it will change how/when we fork in order to address this in the way I am thinking about
- Its also important to know how/when we fork too, I can shed more lights on this

Start at src/lib/branch.js around line 10 and trace the word submission flow, including when the fork and branch are created. Determine how an existing branch is detected and how the submission currently reports failure. Done means duplicate submissions receive a clear message directing users to edit the existing word, with the fork timing understood.

Written by the indexing model from the issue text.