feat(progress): report uncounted status through the sink

A run blocked on the cache-entry flock was silent: the wait went to
the log sink, which renders nowhere by default, so the CLI read as
a hang. The Progress trait gains message() - a status line outside
the counted-operation protocol, defaulting to a no-op so existing
sinks keep compiling - and the flock wait reports what it is
waiting for. The CLI renders messages on the active bar and spins
one up when no operation is active.

crates/ecrou-cli/src/progress.rs

@@ -88,4 +88,24 @@ impl Progress for TermProgress {
             bar.finish_and_clear();
         }
     }
+
+    fn message(&self, text: &str) {
+        let mut slot = self.bar.lock().unwrap();
+        if slot.is_none() {
+            // No operation is active: the message becomes a spinner
+            // until the next `begin` replaces it.
+            let pb = ProgressBar::new_spinner();
+            pb.set_style(
+                ProgressStyle::default_spinner()
+                    .template("{spinner:.green} {msg}")
+                    .unwrap(),
+            );
+            pb.set_message(text.to_string());
+            *slot = Some(pb);
+            return;
+        }
+        if let Some(bar) = &*slot {
+            bar.set_message(text.to_string());
+        }
+    }
 }