refactor(docker): move network.py into platform/docker/

The Docker bridge / internal network primitives are Docker-specific;
they belong inside the Docker platform package alongside util.py and
the rest. Same logic the earlier top-level docker.py move followed.

Imports:
  - platform.py: `from ... import network as network_mod`
                 -> `from . import network as network_mod`
  - network.py: `from .log import ...` -> `from ...log import ...`
  - tests/test_orphan_cleanup.py: from claude_bottle.network
                 -> from claude_bottle.platform.docker.network

tests/test_orphan_cleanup.py

@@ -7,7 +7,7 @@ import os
 import subprocess
 import unittest
 
-from claude_bottle.network import (
+from claude_bottle.platform.docker.network import (
     network_create_egress,
     network_create_internal,
     network_remove,