Refactor useGeminiStream to pull slash commands and passthrough comma… (#215)

* Refactor useGeminiStream to pull slash commands and passthrough commands into their own processors.

* whitespace lint errors.

* Add sugestions from code review.

packages/cli/src/ui/utils/commandUtils.ts

@@ -15,3 +15,12 @@
 export const isPotentiallyAtCommand = (query: string): boolean =>
   // Check if starts with @ OR has a space, then @, then a non-space character.
   query.startsWith('@') || /\s@\S/.test(query);
+
+/**
+ * Checks if a query string represents a slash command (starts with '/').
+ *
+ * @param query The input query string.
+ * @returns True if the query is a slash command, false otherwise.
+ */
+export const isSlashCommand = (query: string): boolean =>
+  query.trim().startsWith('/');