feat(palier-3): recherche globale, mes issues, briefing ntfy, MCP lecture

- client: search_issues (/repos/issues/search, type=issues,
  assigned_by), delete_label + forget_label_cache; models: kv_store
- /search groupe par projet avec colonne Kanban; /my = issues
  ouvertes assignées à l'utilisateur du jeton (get_user)
- briefing: _briefing_data (focus, âgées, milestones <= 7 j,
  activité journal), page /briefing, /api/briefing, envoi ntfy
  manuel + planificateur lifespan à KANBANTE_BRIEFING_TIME
  (kv briefing_last_sent, pas de doublon); app/briefing.py =
  format texte + envoi ntfy (en-têtes ASCII)
- MCP: POST /mcp JSON-RPC (initialize, tools/list, tools/call,
  ping, notifications 202), 7 outils en lecture seule, GET /mcp
  de découverte; erreurs -32601/-32700, isError pour les outils
- focus refactoré en _collect_focus_groups réutilisé par le
  briefing et l'outil MCP get_focus

app/gitea_client.py

@@ -269,6 +269,37 @@ class GiteaClient:
         )
         r.raise_for_status()
 
+    async def delete_label(self, owner: str, repo: str, label_id: int) -> None:
+        """Delete a label definition from the repo (all issues lose it)."""
+        r = await self.client.delete(f"/repos/{owner}/{repo}/labels/{label_id}")
+        r.raise_for_status()
+        self.forget_label_cache(owner, repo)
+
+    def forget_label_cache(self, owner: str, repo: str) -> None:
+        cache = self.__dict__.get("_label_cache")
+        if cache:
+            cache.pop(f"{owner}/{repo}", None)
+
+    # ── Issue search (global + assigned) ───────────────────
+
+    async def search_issues(
+        self,
+        q: str = "",
+        state: str = "open",
+        assigned_by: str | None = None,
+    ) -> list[dict]:
+        """Search issues across every repo visible to the token.
+
+        Uses Gitea's /repos/issues/search (type=issues excludes PRs).
+        Results carry their repository in issue["repository"].
+        """
+        params: dict[str, Any] = {"state": state, "type": "issues"}
+        if q:
+            params["q"] = q
+        if assigned_by:
+            params["assigned_by"] = assigned_by
+        return await self._get_all_pages("/repos/issues/search", **params)
+
     # ── Milestones ─────────────────────────────────────────
 
     async def get_milestones(