Add option to specify custom branch name

Problem

Currently, branch names are always auto-generated from the commit message with no way to override. This can be limiting when:

• The commit message doesn't translate well to a branch name
• User has a specific naming convention
• Multiple commits with similar messages create confusing branch names

Examples from Other Tools

Charcoal:

charcoal create -n my-custom-branch -m "My commit message"

st:

st create my-custom-branch  # Or prompts interactively

Proposed Solution

Add a --name (or -n) flag to the create command:

shortcake create --name my-feature-branch

Implementation Options

Option 1: Flag Only

shortcake create --name custom-branch
# Opens editor, commits, uses 'custom-branch' as name

Option 2: Interactive Fallback

shortcake create
# After commit, show: "Generated branch name: add-new-feature"
# Prompt: "Use this name? [Y/n] (or enter custom name):"

Option 3: Positional Argument

shortcake create [branch-name]
# If provided, use it; otherwise auto-generate

User Stories

• As a developer, I want to use my team's branch naming convention (e.g., feature/TICKET-123-description)
• As a developer, I want to preview the auto-generated name and change it if needed
• As a developer, I want to create branches without committing first (empty branch for future work)

Implementation Notes

Related code: shortcake/cli.py:125-132

Would need to modify the create command to accept an optional name parameter and skip auto-generation if provided.

Start at the create command in shortcake/cli.py:125-132 and trace how the branch name is currently generated. Clarify which proposed interface should be implemented, then make the selected name override or complement auto-generation as specified. Done means the create command supports the agreed custom-branch workflow.