Please explain the motivation behind the feature request.
When using Claude Code as a provider in Goose Desktop, slash commands (such as /t for theme toggling, /help, /plan, etc.) are not recognized or processed correctly. Instead of executing the command, Goose interprets them as regular text input. This is problematic because:

These slash commands are documented as standard features in the Goose CLI and should provide consistent functionality across all interfaces
Users coming from the CLI expect these commands to work in the Desktop client
Important workflow commands like /plan (for reviewing AI intentions), /summarize (for context management), and /recipe (for saving session recipes) are inaccessible
Theme switching via /t would improve readability and user comfort during long coding sessions

This issue specifically occurs when using Claude Code as the provider - the commands are typed but Goose responds as if they're regular conversation text rather than commands.
Describe the solution you'd like
Enable full slash command support in Goose Desktop when using Claude Code (and other CLI providers) as the backend. Specifically:

Recognize and process all documented slash commands (/t, /help, /plan, /summarize, /recipe, /prompt, /mode, etc.)
Provide visual feedback when a slash command is recognized (e.g., syntax highlighting or autocomplete)
Ensure feature parity between Goose CLI and Goose Desktop interfaces
Add slash command documentation/hints in the Desktop UI (perhaps in a help menu or tooltip)

Describe alternatives you've considered

Using Goose CLI instead - This works but loses the benefits of the Desktop GUI (better visual layout, easier session management, integrated file handling)
GUI buttons/menus for commands - Adding UI buttons for common commands like theme switching, but this doesn't solve the problem for power users who prefer keyboard shortcuts
Keyboard shortcuts - Implementing keyboard shortcuts (e.g., Cmd+T for theme toggle) instead of slash commands, though this breaks consistency with the CLI interface

Additional context

This issue occurs specifically with Claude Code as the provider configured via GOOSE_PROVIDER=claude-code
The documentation clearly shows these commands should be available during active sessions
Example of current behavior: Typing /t results in Goose responding "I see you typed '/t' - I'm not sure what specific command or action you're looking for there" instead of toggling the theme
This affects all slash commands, not just theme toggling
Having these commands work would significantly improve the developer experience, especially for users who frequently switch between CLI and Desktop interfaces

• I have verified this does not duplicate an existing feature request