Add vim support to brev open command

Summary

Adds vim support to the brev open CLI command, allowing users to run brev open <instance> vim to SSH into a brev instance and launch vim in the home directory. The implementation follows the established pattern used by tmux support, including automatic installation checking.

Key Changes:

• Added EditorVim = "vim" constant to supported editor types
• Updated validation logic in handleSetDefault() and determineEditorType() to include vim
• Added vim case to openEditorByType() and getEditorName() functions
• Implemented openVim() function that SSHs into instance and launches vim
• Added ensureVimInstalled() function that checks for vim and installs it automatically if missing
• Added vim-specific error handling in runOpenCommand() with informative messages
• Updated help text, examples, and flag descriptions to include vim support

The vim implementation uses the same SSH-based approach as tmux: ssh -t <alias> 'cd <path> && vim'

Review & Testing Checklist for Human

• End-to-end functional test: Test brev open <instance> vim with an actual brev instance to ensure vim launches correctly in the home directory
• Auto-installation test: Test with an instance that doesn't have vim installed to verify automatic installation works and shows appropriate progress messages
• Directory handling: Verify vim opens in the correct directory (home directory by default, or custom directory when using -d flag)
• Error handling: Test error scenarios (network issues, permission problems, etc.) to ensure error messages are helpful
• Regression testing: Test existing editors (code, cursor, windsurf, tmux) to ensure they still work correctly after these changes

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    CLI["brev open <instance> vim"] --> runOpenCommand["runOpenCommand()"]
    runOpenCommand --> determineEditorType["determineEditorType()"]
    determineEditorType --> openEditorByType["openEditorByType()"]
    openEditorByType --> openVim["openVim()"]:::major-edit
    openVim --> ensureVimInstalled["ensureVimInstalled()"]:::major-edit
    ensureVimInstalled --> sshVim["SSH: 'cd $HOME && vim'"]
    
    runOpenCommand --> errorHandling["Error Handling"]:::minor-edit
    errorHandling --> vimNotFound["vim: command not found<br/>Auto-install message"]:::minor-edit
    
    constants["Editor Constants"]:::minor-edit
    validation["Validation Logic"]:::minor-edit
    helpText["Help Text & Examples"]:::minor-edit
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit
        L3[Context/No Edit]:::context
    end

    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

Notes

Implementation follows tmux pattern: The vim support closely mirrors the existing tmux implementation, including the SSH approach, installation checking, and error handling patterns.

Linting note: There's a cyclomatic complexity warning due to additional error handling in runOpenCommand(), but this follows the established pattern used by other editors.

Testing limitation: The implementation couldn't be tested end-to-end during development since it requires actual brev instances to SSH into. Human testing is critical to verify functionality.

Link to Devin run: https://app.devin.ai/sessions/bfdf3682604243ae98caa1a810a5d9d9
Requested by: @theFong