Consolidate GitHub API logic

[codcod]

Problem: The logic for interacting with the GitHub API is split between api.rs and the PrCommand in pr.rs. The command orchestrates git operations and then calls the API.

Suggestion: Encapsulate the entire "create a pull request" flow (including git operations like branch creation, commit, and push) into a single high-level function within the github module, for example, github::create_pr_from_workspace().

Minimal Change Example:

Create a new high-level function in api.rs:

// ...existing code...
/// High-level function to create a PR from local changes
pub async fn create_pr_from_workspace(repo: &Repository, options: &PrOptions) -> Result<()> {
    // 1. Check for changes
    if !git::has_changes(&repo.get_target_dir())? {
        // ... print no changes and return
        return Ok(());
    }

    // 2. Create branch, add, commit, push (move logic from PrCommand::execute)
    // ...

    // 3. Create GitHub PR
    create_github_pr(repo, &branch_name, options).await?;

    Ok(())
}
// ...existing code...

The PrCommand::execute method would then become much simpler, primarily responsible for iterating through repositories and calling this new function.