Give the GitHub GraphQL requests a timeout

The http.Client used for fetching pull requests had no timeout, so on a
network that silently drops packets a request could stay in flight
until the OS-level TCP timeouts kick in, which can take many minutes.
The fetch has no visible status, so nothing tells the user it is still
running; bounding it keeps the refresh's worst case short, and the next
refresh simply tries again.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkg/commands/git_commands/github.go

@@ -210,7 +210,10 @@ func (self *GitHubCommands) fetchRecentPRsAux(endpoint string, repoOwner string,
 	req.Header.Set("Authorization", "token "+token)
 	req.Header.Set("Content-Type", "application/json")
 
-	client := &http.Client{}
+	// Bound the request so that a dead or extremely slow network can't leave
+	// the pull-request refresh in flight for minutes. The data is auxiliary,
+	// so giving up and retrying on the next refresh beats waiting.
+	client := &http.Client{Timeout: 10 * time.Second}
 	resp, err := client.Do(req)
 	if err != nil {
 		return nil, err