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>

property-inspector/giteapr/inspector.html

@@ -20,9 +20,12 @@
       <div class="uspi-item">
         <div class="uspi-item-label" data-localize>PR Filter</div>
         <select class="uspi-item-value" name="filter">
+          <option value="your_repos" data-localize>Your Repositories</option>
           <option value="assigned" data-localize>Assigned to me</option>
+          <option value="created" data-localize>Created by me</option>
           <option value="review_requested" selected data-localize>Review requested</option>
-          <option value="both" data-localize>Both</option>
+          <option value="reviewed" data-localize>Reviewed by me</option>
+          <option value="mentioned" data-localize>Mentioned me</option>
         </select>
       </div>
       <div class="uspi-item">