fix(core,android,app): say why a crawl failed, not only which URL

A transport failure's text is reqwest's "error sending request for url
(…)", and the cause sits further down its source chain. Error::describe
appends the causes and drops the URL, so the reason fits on a share row.

crates/pstr-app/src/engine.rs

@@ -1494,7 +1494,7 @@ impl Engine {
                     if let Err(error) = self
                         .catalog
                         .lock()
-                        .record_crawl_failure(&share_id, &error.to_string())
+                        .record_crawl_failure(&share_id, &error.describe())
                     {
                         tracing::warn!(%error, "record a failed crawl");
                     }