refactor(bottles): move 'list active' onto DockerBottlePlatform

Add list_active() abstract method on BottlePlatform; DockerBottlePlatform
implements it with the existing docker ps logic. cli/list.py no longer
calls docker directly — it just dispatches the active branch to the
platform.

claude_bottle/bottles/__init__.py

@@ -122,6 +122,11 @@ class BottlePlatform(ABC):
     def cleanup(self, plan: BottleCleanupPlan) -> None:
         """Remove everything described by the cleanup plan."""
 
+    @abstractmethod
+    def list_active(self) -> None:
+        """Print every currently-running bottle on this platform to
+        stderr (name + status)."""
+
 
 # Import concrete platform classes AFTER the base types are defined, so
 # each platform module can pull BottleSpec / BottlePlan / BottlePlatform