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>

de_DE.json

@@ -16,9 +16,12 @@
     "Repository": "Repository",
     "API Token": "API Token",
     "PR Filter": "PR-Filter",
+    "Your Repositories": "Eigene Repositories",
     "Assigned to me": "Mir zugewiesen",
+    "Created by me": "Von mir erstellt",
     "Review requested": "Review angefordert",
-    "Both": "Beides",
+    "Reviewed by me": "Von mir bewertet",
+    "Mentioned me": "Hat mich erwähnt",
     "Server": "Server",
     "Last Rised": "Letzter Anstieg",
     "Pull Requests": "Pull Requests",