feat: UI de configuration des colonnes et mappings label→colonne

- Bouton ⚙ sur chaque colonne pour configurer le mapping label Gitea
- Modal ⚙ Colonnes pour ajouter/renommer/supprimer des colonnes
- API DELETE /api/col-mapping pour supprimer un mapping
- Rafraîchit le board après chaque modification de colonne/mapping
- CSS pour les nouveaux éléments (config panel, column list)

app/routers/api.py

@@ -195,6 +195,31 @@ async def set_col_mapping(
     return {"status": "ok", "column": column, "label": gitea_label}
 
 
+@router.delete("/col-mapping")
+async def delete_col_mapping(
+    owner: str = Query(...),
+    repo: str = Query(...),
+    column: str = Query(...),
+):
+    """Delete a column-to-label mapping."""
+    with get_conn() as conn:
+        board = conn.execute(
+            "SELECT id FROM boards WHERE project_owner=? AND project_name=?",
+            (owner, repo),
+        ).fetchone()
+        if not board:
+            raise HTTPException(status_code=404, detail="Board not found")
+        board_id = board["id"]
+
+        conn.execute(
+            "DELETE FROM col_mapping WHERE board_id=? AND column_name=?",
+            (board_id, column),
+        )
+        conn.commit()
+
+    return {"status": "ok", "column": column}
+
+
 @router.get("/board-config/{owner}/{repo}")
 async def get_board_config(owner: str, repo: str):
     with get_conn() as conn: