Quadruple all HTTP timeouts to prevent timeout errors

- HTTP request timeout: 2s -> 8s
- Stats collection context timeout: 1s -> 4s
- HTTP read header timeout: 10s -> 40s

This should prevent timeout errors when the database is under load
or when complex queries take longer than expected (slow query
threshold is 50ms).

internal/server/routes.go

@@ -16,7 +16,7 @@ func (s *Server) setupRoutes() {
 	r.Use(middleware.RealIP)
 	r.Use(middleware.Logger)
 	r.Use(middleware.Recoverer)
-	const requestTimeout = 2 * time.Second
+	const requestTimeout = 8 * time.Second
 	r.Use(TimeoutMiddleware(requestTimeout))
 	r.Use(JSONResponseMiddleware)