feat(palier-1): journal d'événements, détail d'issue, vieillissement, WIP

- board_events append-only + log_event/get_events/column_entry_times/
  get_metrics (débit, temps de cycle); journalisation des moves,
  créations, fermetures/rouvertures (UI et réconciliation Gitea),
  commentaires; un reclassement intra-colonne ne journalise pas
- client Gitea: get_issue, get_issue_comments (paginés), create_comment
- API: GET /api/issues/{o}/{r}/{n} (404 propre), POST .../comments,
  GET /api/events, GET /api/metrics, page /activity
- config: KANBANTE_WIP_LIMITS (colonne:limite) et KANBANTE_AGING_DAYS;
  le board calcule le temps en colonne (journal, replis updated_at
  puis création de l'issue)
- reconcile_board_state retourne aussi les numéros fermés/purgés

app/gitea_client.py

@@ -198,6 +198,29 @@ class GiteaClient:
                 issues_by_repo[full_name] = []
         return issues_by_repo
 
+    async def get_issue(self, owner: str, repo: str, number: int) -> dict:
+        """One issue with body, labels, assignees, milestone."""
+        return await self._get(f"/repos/{owner}/{repo}/issues/{number}")
+
+    async def get_issue_comments(
+        self, owner: str, repo: str, number: int
+    ) -> list[dict]:
+        """All comments of an issue (paginated)."""
+        return await self._get_all_pages(
+            f"/repos/{owner}/{repo}/issues/{number}/comments"
+        )
+
+    async def create_comment(
+        self, owner: str, repo: str, number: int, body: str
+    ) -> dict:
+        """Post a comment on an issue and return it."""
+        r = await self.client.post(
+            f"/repos/{owner}/{repo}/issues/{number}/comments",
+            json={"body": body},
+        )
+        r.raise_for_status()
+        return r.json()
+
     async def create_issue(
         self, owner: str, repo: str, title: str, body: str = ""
     ) -> dict: