improve Gitea PR plugin with correct filter options

- Replace custom filters with Gitea UI equivalents (your repos, assigned,
  created, review requested, reviewed, mentioned)
- Fix pagination to fetch all pages from issues/search
- Filter out false-positive issues (pull_request: null)
- Use issues/search API for all filters (correct token scopes required)
- Add StreamAction registration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugin/app.html

@@ -18,6 +18,7 @@
   <script src="./actions/GiteaAction.js"></script>
   <script src="./actions/GiteaPRAction.js"></script>
   <script src="./actions/RailwayAction.js"></script>
+  <script src="./actions/StreamAction.js"></script>
   <script src="./app.js"></script>
 </body>
 </html>