fix(board): les issues réelles Gitea n'étaient pas des PR — boards vides

Gitea 1.27.3 renvoie "pull_request": null sur les issues ordinaires:
_is_issue testait la présence de la clé et classait chaque vraie
issue comme un pull request. Board, Focus et briefing affichaient
zéro carte contre un vrai Gitea (le dashboard, basé sur les
compteurs de dépôts, semblait normal, d'où le signalement
« la nouvelle issue n'apparaît pas »). Le filtre teste maintenant
la valeur. Vérifié en réel: board bruno/flowdeck 0 -> 6 cartes.

app/gitea_client.py

@@ -172,8 +172,10 @@ class GiteaClient:
     ) -> list[dict]:
         """Get issues for a repo (paginated, cached).
 
-        Note: Gitea's issues endpoint also returns pull requests; each
-        PR carries a "pull_request" key and callers filter on it.
+        Note: Gitea's issues endpoint also returns pull requests; a
+        PR carries a non-null "pull_request" object, a plain issue
+        carries "pull_request": null — callers filter on truthiness
+        (see app.main._is_issue).
         """
         key = f"issues:{owner}/{repo}:{state}"
         cached = self._cache_get(key)

app/main.py

@@ -323,8 +323,15 @@ def classify_repos(
 
 
 def _is_issue(item: dict) -> bool:
-    """Gitea's issues endpoint also returns PRs; they carry this key."""
-    return "pull_request" not in item
+    """True for issues, False for pull requests.
+
+    Gitea's issues endpoint also returns PRs. A PR carries a
+    ``pull_request`` *object*; a plain issue carries the same key
+    with value ``null`` (verified against Gitea 1.27.3). Testing key
+    presence therefore classifies every real issue as a PR and
+    empties the board — test the value's truthiness instead.
+    """
+    return not item.get("pull_request")
 
 
 def _merge_issues_with_board(