Fix sparkline service name mapping

- Pass service names (not slugs) to DockerStatsCollector
- Create slug->name mapping for sparkline lookups
- Stats are stored by service name, looked up by slug
- Add debug logging when no containers found

src/textual_webterm/docker_stats.py

@@ -201,7 +201,7 @@ class DockerStatsCollector:
         refresh_counter = 0
 
         while self._running:
-            # Refresh container mapping every 30 iterations (~60 seconds)
+            # Refresh container mapping every 30 iterations (~5 minutes at 10s interval)
             if refresh_counter % 30 == 0:
                 service_to_container = await self._discover_containers(service_names)
                 if service_to_container:
@@ -209,6 +209,11 @@ class DockerStatsCollector:
                         "Discovered containers: %s",
                         ", ".join(f"{k}={v}" for k, v in service_to_container.items()),
                     )
+                else:
+                    log.debug(
+                        "No containers found for services: %s",
+                        ", ".join(service_names),
+                    )
 
             refresh_counter += 1