refactor: split services/docker.py into focused modules (Task 3.3)

- Create services/docker/compose.py — compose file generation and commands
- Create services/docker/container.py — container lifecycle and queries
- Create services/docker/config_staging.py — config folder file writing
- Create services/docker/tunnel.py — Cloudflare tunnel management
- Create services/docker/__init__.py — barrel exports
- Delete services/docker.py (replaced by package)
- All imports in api/tool_instances.py remain functional

Quality gates: Python syntax check (pass), imports verified
Refs: repo-restructure Task 3.3

apps/api/src/services/docker/__init__.py

@@ -0,0 +1,44 @@
+"""Docker services for container and tunnel management."""
+
+from .compose import (
+    ensure_instance_directory,
+    execute_compose_command,
+    render_compose_template,
+    write_compose_file,
+    write_env_file,
+)
+from .config_staging import write_config_files, write_config_folder_files
+from .container import (
+    connect_container_to_network,
+    find_free_port,
+    get_container_id,
+    get_container_logs,
+    get_container_name,
+    get_container_status,
+)
+from .tunnel import (
+    check_tunnel_health,
+    recreate_tunnel,
+    start_cloudflared_tunnel,
+    stop_cloudflared_tunnel,
+)
+
+__all__ = [
+    "render_compose_template",
+    "ensure_instance_directory",
+    "write_compose_file",
+    "write_env_file",
+    "execute_compose_command",
+    "write_config_files",
+    "write_config_folder_files",
+    "get_container_id",
+    "get_container_name",
+    "connect_container_to_network",
+    "get_container_status",
+    "get_container_logs",
+    "find_free_port",
+    "start_cloudflared_tunnel",
+    "stop_cloudflared_tunnel",
+    "recreate_tunnel",
+    "check_tunnel_health",
+]