feat: Add context argument to completion handlers

This commit adds a `context` argument to the completion handlers in `PromptsTab`, `ResourcesTab`, `useCompletionState`, and `useConnection`.

The context argument allows passing additional information to the completion engine, which can be used to improve the quality of the completions.  The context is passed as a dictionary of key-value pairs.

The `ResourcesTab` component was also updated to pass `templateValues` as the `context` to the completion handler.

The `useConnection` hook was updated to include the context in the completion request sent to the server.

client/src/lib/hooks/useConnection.ts

@@ -170,6 +170,7 @@ export function useConnection({
     ref: ResourceReference | PromptReference,
     argName: string,
     value: string,
+    context?: Record<string, string>,
     signal?: AbortSignal,
   ): Promise<string[]> => {
     if (!mcpClient || !completionsSupported) {
@@ -187,6 +188,12 @@ export function useConnection({
       },
     };
 
+    if (context) {
+      request["params"]["context"] = {
+        arguments: context,
+      };
+    }
+
     try {
       const response = await makeRequest(request, CompleteResultSchema, {
         signal,