Feature Request: Allow Tab key for smart completion navigation

### Description:

Currently, when using WindTerm's smart completion (e.g., for command history or path completion), navigating through the suggestions list is done exclusively using the Up and Down arrow keys. While the Tab key is often used to complete the currently highlighted suggestion or to list all available suggestions, many users are accustomed to a different workflow where Tab is also leveraged for navigation.
This current behavior requires users to move their hands to the arrow keys for list navigation, which can interrupt typing flow and feel less efficient compared to staying on the main keyboard area.
### Describe the solution I like
I would like to request an option to remap the key bindings for smart completion navigation and selection to allow for the following workflow:
Tab key: Pressing Tab should navigate forward (downwards) through the smart completion suggestion list.
Shift+Tab key: Pressing Shift+Tab should navigate backward (upwards) through the smart completion suggestion list.
Enter key: Pressing Enter should select and insert the currently highlighted suggestion into the command line.
This would provide a highly efficient and familiar interaction model for users coming from various IDEs and advanced shell environments where Tab is frequently used for cycling through suggestions.
### Describe alternatives I considered
I have tried looking through WindTerm's current settings and keymap configurations but could not find an option to customize the navigation and selection keys for smart completion in this manner. The default Up/Down arrow navigation and Tab for completion behavior is understandable, but offering this alternative configuration would significantly improve the user experience for those who prefer Tab-based navigation.
### Additional context
Many modern IDEs (like VS Code, IntelliJ IDEA) and advanced shell environments (with certain plugins or configurations) allow Tab and Shift+Tab for cycling through auto-completion suggestions, and Enter for selection. Adopting this pattern as a configurable option would offer a more consistent and potentially faster workflow, reducing the need for hand movement away from the primary typing keys.
I am currently using WindTerm version 2.7.0_Mac_Portable_x86_64
Thank you for considering this feature request!

Start by locating WindTerm's smart completion key handling and its keymap or settings configuration, then verify the existing Up/Down, Tab, and Enter behavior. Done means users can configure Tab to move forward, Shift+Tab backward, and Enter to select the highlighted suggestion without losing existing behavior.

Written by the indexing model from the issue text.