fix: GitHub list_issues built the wrong URL for org-owned repos

Used format!("repos/{owner}/{repo}/issues", ...) instead of the
slug() helper list_pull_requests already uses, so an org-owned repo
(passed as 'Org/repo') produced repos/{personal_owner}/Org/repo/issues
— a 404 the code silently swallows into an empty list, making the
Issues tab look like 'no issues' instead of a broken request.

src/providers/github.rs

@@ -418,8 +418,8 @@ impl Provider for GitHubProvider {
     async fn list_issues(&self, repo: &str) -> Result<Vec<IssueDetail>> {
         let resp = self.client
             .get(self.url(&format!(
-                "repos/{}/{}/issues?state=open&per_page=100&pulls=false",
-                self.owner, repo
+                "repos/{}/issues?state=open&per_page=100&pulls=false",
+                self.slug(repo)
             )))
             .send().await?;
         if !resp.status().is_success() { return Ok(vec![]); }