fix(sqlite,browser): resolve SQLite connection pool deadlock, disable stale SW cache, and update BRAIN.md

internal/api/server.go

@@ -112,8 +112,19 @@ func (s *Server) Router() http.Handler {
 				path = "index.html"
 			}
 			if _, err := fs.Stat(s.staticFS, path); err != nil {
+				// Never return index.html for missing JS/CSS assets
+				if strings.HasPrefix(path, "assets/") || strings.HasSuffix(path, ".js") || strings.HasSuffix(path, ".css") {
+					http.NotFound(w, req)
+					return
+				}
 				// SPA client-side routing fallback to index.html
 				req.URL.Path = "/"
+				path = "index.html"
+			}
+			if path == "index.html" || path == "sw.js" || path == "manifest.json" {
+				w.Header().Set("Cache-Control", "no-store, no-cache, must-revalidate")
+				w.Header().Set("Pragma", "no-cache")
+				w.Header().Set("Expires", "0")
 			}
 			fileServer.ServeHTTP(w, req)
 		})
@@ -126,6 +137,7 @@ func (s *Server) Router() http.Handler {
 
 func writeJSON(w http.ResponseWriter, status int, data interface{}) {
 	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.Header().Set("Cache-Control", "no-store, no-cache, must-revalidate")
 	w.WriteHeader(status)
 	_ = json.NewEncoder(w).Encode(data)
 }