fix: take the file edit limit in the panel from the agent's read cap

The limit was repeated in the page; a file of exactly the cap is read
in full, so it is editable too.

internal/server/handlers_panel_fs.go

@@ -34,7 +34,7 @@ func (s *Server) handleFilesPage(w http.ResponseWriter, r *http.Request) {
 		http.NotFound(w, r)
 		return
 	}
-	s.render(w, "files.html", map[string]any{"Agent": a})
+	s.render(w, "files.html", map[string]any{"Agent": a, "EditLimit": proto.FSReadCap})
 }
 
 // POST /api/panel/agents/{id}/fs/{op} — run a file-manager operation on the